Fission reaction control in a molten salt reactor

ABSTRACT

A molten salt reactor includes a nuclear reactor core for sustaining a nuclear fission reaction fueled by a molten fuel salt. A molten fuel salt control system removes a volume of the molten fuel salt from the nuclear reactor core to maintain a reactivity parameter within a range of nominal reactivity. The molten fuel salt control system includes a molten fuel salt exchange system that fluidically couples to the nuclear reactor core and exchanges a volume of the molten fuel salt with a volume of a feed material containing a mixture of a selected fertile material and a carrier salt. The molten fuel salt control system can include a volumetric displacement control system having one or more volumetric displacement bodies insertable into the nuclear reactor core. Each volumetric displacement body can remove a volume of molten fuel salt from the nuclear reactor core, such as via a spill-over system.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation of U.S. patent applicationSer. No. 14/981,606, entitled “Fission Reaction Control in a Molten SaltReactor”, issued on Oct. 8, 2019 as U.S. Pat. No. 10/438705.

U.S. patent application Ser. No. 14/981,606 claims priority to U.S.Provisional Patent Application No. 62/098,984, entitled “Molten SaltNuclear Reactor and Method of Controlling the Same” and filed on Dec.31, 2014, and U.S. Provisional Patent Application No. 62/234,889,entitled “Molten Chloride Fast Reactor and Fuel” and filed on Sep. 30,2015, both of which are specifically incorporated herein for all thatthey disclose and teach.

U.S. patent application Ser. No. 14/981,606 also claims priority to U.S.Provisional Patent Application No. 62/097,235, entitled “TargetryCoupled Separations” and filed on Dec. 29, 2014, which is specificallyincorporated herein for all that it discloses and teaches.

U.S. patent application Ser. No. 14/981,606 is also related to U.S.patent application Ser. No. 14/981,512, entitled “Molten Nuclear FuelSalts and Related Systems and Methods” and filed on Dec. 28, 2015, whichis specifically incorporated herein for all that it discloses andteaches.

BACKGROUND

Molten salt reactors (MSRs) identify a class of nuclear fission reactorsin which the fuel and coolant are in the form of a molten salt mixturecontaining solid or dissolved nuclear fuel, such as uranium or otherfissionable elements. One class of MSR is a molten chloride fast reactor(MCFR), which uses a chloride-based fuel salt mixture that offers a highuranium/transuranic solubility to allow a more compact system designthan other classes of MSRs. The design and operating parameters (e.g.,compact design, low pressures, high temperatures, high power density) ofan MCFR offer the potential for a cost-effective, globally-scalablesolution to zero carbon energy.

SUMMARY

The described technology provides a molten salt reactor including anuclear reactor core configured to contain a nuclear fission reactionfueled by a molten fuel salt. A molten fuel salt control system coupledto the nuclear reactor core is configured to remove a selected volume ofthe molten fuel salt from the nuclear reactor core to maintain aparameter indicative of reactivity of the molten salt reactor within aselected range of nominal reactivity.

In one implementation, a molten salt reactor including a nuclear reactorcore configured to sustain a nuclear fission reaction fueled by a moltenfuel salt. The molten fuel salt control system includes a molten fuelsalt exchange system that fluidically couples to the nuclear reactorcore and is configured to exchange a selected volume of the molten fuelsalt with a selected volume of a feed material containing a mixture of aselected fertile material and a carrier salt. In another implementation,the molten fuel salt control system includes a volumetric displacementcontrol system having one or more volumetric displacement bodiesinsertable into the nuclear reactor core. Each volumetric displacementbody is configured to volumetrically displace a selected volume ofmolten fuel salt from the nuclear reactor core when inserted into thenuclear reactor core. In one implementation, the volumetric displacementbody removes the selected volume of molten fuel salt from the nuclearreactor core, such as via a spill-over system.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter.

Other implementations are also described and recited herein.

BRIEF DESCRIPTIONS OF THE DRAWINGS

FIG. 1 schematically illustrates an example molten chloride fast reactor(MCFR) fuel cycle with a MCFR parent reactor and a MCFR daughterreactor.

FIG. 2 illustrates example MCFR reactivity control resulting fromperiodic molten fuel removal of molten fuel salt and replacement with afertile molten fuel feed, referred to as molten fuel salt exchange.

FIG. 3 illustrates an example MCFR system equipped with a molten fuelsalt exchange assembly.

FIG. 4 illustrates a graph of modeled k_(eff) values of a reactor coreand the total percentage of burn up of heavy metal (HM) fuel over timefor a molten salt reactor controlled by the periodic exchange of moltenfuel salt of the reactor with a fertile fuel salt.

FIG. 5 illustrates a graph of k_(eff) versus time for a modeled moltensalt reactor with a depleted uranium feed provided at a rate thatmatches the reactor burn rate.

FIG. 6 illustrates a graph depicting k_(eff) as function of time for amolten salt reactor with no addition of feed material and no removal oflanthanides.

FIG. 7 illustrates an alternative example MCFR system equipped with amolten fuel salt exchange assembly.

FIG. 8 illustrates an example ternary phase diagram for UCl₃-UCl₄-NaCl(in mole %).

FIG. 9 illustrates example operations for a molten fuel salt exchangeprocess.

FIG. 10 illustrates a molten salt reactor equipped with a displacementelement assembly.

FIG. 11 illustrates a molten salt reactor equipped with a displacementelement assembly and a molten fuel salt spill-over system with adisplacement element not submerged in molten fuel salt.

FIG. 12 illustrates a molten salt reactor equipped with a displacementelement assembly and a molten fuel salt spill-over system with adisplacement element submerged in molten fuel salt.

FIG. 13 illustrates various example stages of a fuel displacement cycle.

FIG. 14 illustrates two example stages of a fuel displacement cycle.

FIG. 15 illustrates example operations for a molten fuel saltdisplacement process.

DETAILED DESCRIPTIONS

A molten salt fast reactor system employs a molten fuel salt in a fastneutron spectrum fission reactor. One type of molten salt reactorincludes a fluoride salt as the carrier salt for the fissile fuel.Another type of molten salt reactor is a molten chloride fast reactor(MCFR) with a chloride salt as the carrier salt for the fissile fuel.Although the below description is written with respect to a molten saltchloride reactor, it is to be appreciated that the description,components, and methods described herein may be applicable to any moltenfuel salt reactor.

In an MCFR system, the fast neutron spectrum provided by chloride saltsenables good breed-and-burn performance using the uranium-plutonium fuelcycle. The fast neutron spectrum also mitigates fission productpoisoning to provide exceptional performance without online reprocessingand the attendant proliferation risks. During operation of an MCFRsystem, a molten fuel salt control system allows maintenance of fuelreactivity and/or fuel composition within desired operational bounds. Inone implementation, the molten fuel salt control system includes amolten fuel salt exchange system that removes molten fuel salt from thenuclear reactor core, such as to maintain a parameter indicative ofreactivity within a selected range of a nominal reactivity. In anadditional or alternative implementation, a molten fuel salt controlsystem includes a volumetric displacement control assembly to removemolten fuel salt from a nuclear reactor to control the fission reactionin the MCFR system (e.g., to maintain a parameter indicative ofreactivity within a selected range of a nominal reactivity). Thevolumetric displacement control assembly may contain or be formed ofnon-neutron absorbing materials, neutron absorbing materials, and/ormoderators.

FIG. 1 schematically illustrates an example molten chloride fast reactor(MCFR) fuel cycle 100 with a MCFR parent reactor 102 and a MCFR daughterreactor 104. A particular classification of fast nuclear reactor,referred to as a “breed-and-burn” fast reactor, is a nuclear reactorcapable of generating more fissile nuclear fuel than it consumes. Forexample, the neutron economy is high enough to breed more fissilenuclear fuel (e.g., plutonium-239) from fertile nuclear reactor fuel(e.g., uranium-238) than it burns. The “burning” is referred to as“burn-up” or “fuel utilization” and represents a measure of how muchenergy is extracted from the nuclear fuel. Higher burn-up typicallyreduces the amount of nuclear waste remaining after the nuclear fissionreaction terminates.

The example MCFR fuel cycle 100 is designed to use molten salt as acarrier for the fissile fuel in the reactor(s). In one example, thiscarrier salt may include one or more of a sodium salt, a chloride salt,a fluoride salt, or any other appropriate molten fluid to carry thefissile fuel through the reactor core. In one example, the moltenchloride salt includes a ternary chloride fuel salt, although otherchloride salts may be employed alternative to or in addition to theternary chloride salt, including without limitation binary, ternary andquaternary chloride fuel salts of uranium and various fissionablematerials. Various compositions have been explored through modelling andtesting with a focus on high actinide concentrations and a resultingcompact reactor size. For example, bred plutonium can exist as PuCl₃within the MCFR fuel cycle 100, and reduction-oxidation control can bemaintained by adjusting the ratio of the oxidation states of thechloride salt used as fertile feed material.

The example MCFR fuel cycle 100 enables an open breed-and-burn fuelcycle (e.g., exhibiting equilibrium, quasi-equilibrium, and/ornon-equilibrium breed-and-burn behavior) employing a uranium-plutoniumfuel cycle and resulting in significantly lower volumes of waste than aconventional open fuel cycle. Various implementations of the describedtechnology provide for a molten fuel salt having a uranium tetrachloride(UCl₄) content level above 5% by molar fraction, which aids inestablishing high heavy metal content in the molten fuel salt (e.g.,above 61% by weight). Uranium tetrachloride implementations may beaccomplished through a mixture of UCl₄ and uranium trichloride (UCL₃)and/or an additional metal chloride (e.g., NaCl), such that desirableheavy metal content levels and melting temperatures (e.g., 330°-800° C.)are achieved.

In one implementation, the MCFR parent reactor 102 includes a reactorvessel designed to hold the molten fuel salt as a reactor core section,one or more heat exchangers, control systems, etc. In oneimplementation, the reactor vessel may have a circular cross-sectionwhen cut along a vertical or Z-axis (i.e., yielding a circularcross-section in the XY plane), although other cross-sectional shapesare contemplated including without limitation ellipsoidal cross-sectionsand polygonal cross-sections. The MCFR parent reactor 102 is startedwith a loading into the reactor vessel an enriched fuel charge ofinitial molten fuel 106, such as using uranium-235 as a startup fuel,such as in the form of UCl₄ and/or UCl₃, along with a carrier salt(e.g., NaCl). In one example, the initial molten fuel 106 mixturecontains enriched uranium at 12.5 w %, although other compositions maybe employed. The initial molten fuel 106 circulates through a reactorcore section in the reactor vessel of the MCFR parent reactor 102. Inone implementation of the MCFR parent reactor 102, the molten fuel saltflows in an upward direction as it is heated by the fission reaction inthe internal central reactor core section and downward around theinternal periphery of the reactor vessel as it cools. It is to beappreciated that other additional or alternative molten fuel flows mayalso be employed (such as the primary coolant loop 313 of FIG. 3) thatare designed to use the convention flows of a heated fluid and gravity,and/or assisted fluid flows through values, pumps, and the like. Theconstituent components of the molten fuel are well-mixed by the fastfuel circulation flow (e.g., one full circulation loop per second). Inone implementation, one or more heat exchangers are positioned at theinternal periphery of the reactor vessel to extract heat from the moltenfuel flow, further cooling the downward flow, although heat exchangersmay additionally or alternatively be positioned outside the reactorvessel.

After initial startup, the MCFR parent reactor 102 reaches criticalityin nuclear fission and the initial fissile fuel (e.g., enriched uranium)converts the fertile fuel to fissile fuel (breeds up). In the example ofinitial fissile fuel including enriched uranium, this fissile enricheduranium can breed depleted and/or natural uranium up to another fissilefuel, e.g., plutonium. This breed-and-burn cycle can breed enoughplutonium-239 fissile nuclear fuel (e.g., in the form of PuCl₃) to notonly operate for decades but to also supply fuel for the MCFR daughterreactor 104 and other daughter and granddaughter reactors. Althoughother daughter and/or granddaughter reactors are not shown, it is to beappreciated that multiple reactors may be fed by the removed used fuelfrom the parent reactor 102 to one or more daughter reactors, which maythen feed start up material to one or more granddaughter reactors, andon and on. In one implementation, the MCFR parent reactor 102 operatesat 1000 MW_(t), which corresponds to a natural fuel circulation pointdesign, although other operating outputs are achievable under differentoperating conditions, including forced fuel circulation to achievehigher thermal power levels. Other fertile fuels may include withoutlimitation used nuclear fuel or thorium.

As previously suggested, during normal operations, the MCFR parentreactor 102 breeds with sufficient efficiency to support a graduallyincreasing reactivity. The MCFR parent reactor 102 can be maintained atcritical (e.g., barely critical) by removing molten fuel salt 108 (whichmay contain fissile fuel, fertile fuel, carrier salt, and or fissionproducts) from the MCFR parent reactor 102 and replacing the removedmolten fuel salt 108 with fertile fuel salt at a slow rate. In thismanner, reactivity can be controlled by periodic removal of a volume offully mixed molten fuel salt that circulates within the reactor vessel,depicted as removed molten fuel 108, and periodic replacement of theremoved molten fuel 108 with depleted uranium chloride salt, depicted asfertile molten fuel feed 110. Other fertile fuels may include withoutlimitation natural uranium, used nuclear fuel or thorium.

In one implementation, the removed molten fuel 108 can be prepared fordisposal as waste or it can be stored until sufficient material isavailable to start a new MCFR plant (e.g., the MCFR daughter reactor104). In some cases, the removed molten fuel 108 can be used to start orinitiate the MCFR daughter plant without reprocessing the removed moltenfuel 108. In the latter scenario, it may be possible for nearly allactinides to move to the next MCFR plant for additional burn-up, thusavoiding proliferation risks associated with nuclear waste. Furthermore,the molten fuel salt exhibits a large negative temperature coefficient,very low excess reactivity, and passive decay heat removal, whichcombine to stabilize the fission reaction.

The MCFR parent reactor 102 outputs certain waste components,illustrated as waste 112. In one implementation, the waste 112 does notcontain actinides. Instead, the waste 112 includes gaseous and possiblyvolatile chloride fission products 114 and solid fission products 116,such as noble metals. The waste 112 can be captured through mechanicalfiltering and/or light gas sparging or any other appropriate techniqueto filter waste 112 from the molten fuel salt while the MCFR parentreactor 102 is in operation or the removed molten fuel 108 may beseparated, treated, and re-introduced to the reactor. The mechanicalfiltering captures the solid fission products 116 and other particulatesthat are less soluble in the molten fuel salt. Similarly, noble fissionproduct gasses are captured and allowed to decay in holding tanks. Thefilters containing the insoluble and longer lived solid fission products116 form a portion of the waste stream. In one implementation, the waste112 also reduces or eliminates criticality concerns as the waste 112does not contain fissile isotopes separated from the fuel salt.

The waste 112 components may include any one or more of transmutationproducts of the nuclear fission or any one of its decay products,chemical reaction products of the fuel salt with other fission products,corrosion products, etc. The elemental components of the waste 112 (alsogenerally called fission products herein) are based upon the elementalcomponents of the fuel salt, carrier salt, components and coatings, etc.For a molten chloride salt, fission products may include any one or moreof noble gases and/or other gases including Iodine, Cesium, Strontium,halogens, tritium, noble and semi-noble metals in aerosol form, and thelike. Solid waste fission products may include noble metals, semi-noblemetals, alkali elements, alkali earth elements, rare earth elements,etc. and molecular combinations and thereof

FIG. 2 illustrates example MCFR reactivity control resulting fromperiodic molten fuel removal of molten fuel salt and replacement with afertile molten fuel feed material, referred to as molten fuel saltexchange. Molten fuel salt exchange systems represent a type of moltenfuel salt control system. The X-axis 200 represents time in effectivefull power years, and the Y-axis represents reactivity in terms ofmodeled k-effective 202. The parameter, k-effective, represents themultiplication factor, which indicates the total number of fissionevents during successive cycles of the fission chain reaction. Each dropin k-effective, such as drops 204, 206, and 208, represents a moltenfuel salt exchange event. By replacing bred up or fissile molten fuelsalt within the reactor with a fertile molten fuel feed, the MCFR can bemaintained within a threshold level of a nominal reactivity. In somecases, the nominal reactivity is at an average near-zero excessreactivity operating condition with an upper threshold defining amaximum reactivity of that fuel cycle to trigger a molten fuel exchange,and the lower threshold defining the minimum reactivity to be achievedafter the molten fuel exchange. The nominal, upper threshold, and/orlower threshold reactivity levels may stay the same or change over thelifetime of the MCFR based upon design, operation, and/or safetyparameters. These parameters, which are indicative of reactivity, mayinclude, without limitation, thermal energy desired to be generated bythe reactor, safety levels, component design and lifetime constraints,maintenance requirements, etc. It should be understood that otherreactivity control techniques may be employed in combination with moltenfuel salt exchange, including without limitation use of a volumetricdisplacement assembly, neutron-absorbing control assemblies, etc.Furthermore, other molten salt reactors may employ a similar molten fuelexchange feature.

As illustrated in FIG. 2, the periodic replacement of molten fuel saltwith the fertile molten fuel feed may be used to limit reactivity andmaintain ongoing breed-and-burn behavior within the reactor.Chronologically, the initial enriched fuel charge of molten fuel saltand fertile molten fuel salt can breed up, thereby increasing thereactivity within the reactor. After the reactor breads up, the periodicremoval of fissile material acts to periodically (whether with uniformor non-uniform periods over time) reduce or control the reactivity ofthe reactor, returning the reactivity of the molten fuel salt back to anacceptable and pre-selected threshold level which may be a criticalcondition 210 (e.g., a barely critical condition) at each molten fuelsalt exchange operation to approximate an average near-zero excessreactivity operating condition. This exchange operation can be repeatedover time, resulting in the “saw tooth” reactivity curve, such as thatshown in the MCFR reactivity control graph of FIG. 2. In someimplementations, periodic exchange operations can allow the reactor tooperate indefinitely without adding supplemental enriched fuel material.While molten fuel salt exchange is described as periodic, it should beunderstood that such exchange may be performed in a batch-wise,continuous, semi-continuous (e.g., drip) manner, etc. It is to beappreciated that increasing the frequency (which may be paired withsmaller volumes of removed bred up fuel) can tighten the control orthresholds around the nominal reactivity to which the MCFR iscontrolled.

FIG. 3 illustrates an example MCFR system 300 equipped with a moltenfuel salt exchange assembly 301. In one implementation, the MCFR system300 includes a reactor core section 302. The reactor core section 302(which may also be referred to as a “reactor vessel”) includes a moltenfuel salt input 304 and a molten fuel salt output 306. The molten fuelsalt input 304 and the molten fuel salt output 306 are arranged suchthat, during operation, a flow of molten fuel salt 308 may form orinclude conical sections acting as converging and diverging nozzles,respectively. In this regard, the molten fuel salt 308 is fluidicallytransported through the volume of the reactor core section 302 from themolten fuel salt input 304 to the molten fuel salt output 306.

The reactor core section 302 may take on any shape suitable forestablishing criticality within the molten fuel salt 308 within thereactor core section 302. As shown in FIG. 3, the reactor core section302 may be in the form of an elongated core section and may having acircular cross-section when cut along a vertical or Z-axis (i.e., acircular cross-section in the XY plane), although other cross-sectionalshapes are contemplated including without limitation ellipsoidalcross-sections and polygonal cross-sections.

The dimensions of the reactor core section 302 are selected such thatcriticality is achieved within the molten fuel salt 308 when flowingthrough the reactor core section 302. Criticality refers to a state ofoperation in which the nuclear fuel sustains a fission chain reaction,i.e., the rate of production of neutrons in the fuel is at least equalto rate at which neutrons are consumed (or lost). For example, in thecase of an elongated core section, the length and cross-sectional areaof the elongated core section may be selected in order to establishcriticality within the reactor core section 302. It is noted that thespecific dimensions necessary to establish criticality are at least afunction of the type of fissile material, fertile material and/orcarrier salt contained within the example MCFR system 300.

As part of the reactor startup operation, the example MCFR system 300 isloaded with an initial enriched fuel charge of molten fuel salt. Thereactor startup operation initiates a fission reaction with abreed-and-burn fuel cycle. The reactivity of the fission reaction of theexample MCFR system 300 increases over time (see FIG. 2.). Whenreactivity fails to satisfy an acceptable reactivity condition (e.g.,k-effective meets or exceeds a threshold, such as an upper threshold of1.005, as indicated in the example shown in FIG. 2), also referred to asan “exchange condition” or a “control condition,” a selected volume ofmolten fuel salt 308 is removed from the reactor core section 302 and aselected volume and composition of fertile molten fuel feed 310 (e.g., asalt loaded with fertile material, such as depleted and/or naturaluranium, used nuclear fuel or thorium.) is loaded into the reactor coresection 302 in place of the removed molten fuel salt 308. The removedmolten fuel salt 308 may include without limitation one or more of thefollowing: lanthanides, other fission products, fissile material,fertile material and/or carrier salt. It is noted that a non-specificremoval of lanthanides reduces the fission product inventory reactorcore section 302 and the associated poisoning but also removes some ofthe fissile material from the reactor core section 302.

In FIG. 3, the molten fuel salt exchange assembly 301 is operablycoupled to the reactor core section 302 (or another portion of theexample MCFR system 300) and is configured to periodically replace aselected volume of the molten fuel salt 308 with a selected volume andcomposition of the feed material 310. In this regard, the molten fuelsalt exchange assembly 301 can control the reactivity and/or compositionof the molten fuel salt 308 within the example MCFR system 300. Thecomposition of the molten fuel salt 308 influences the oxidation statesof the molten fuel salt 308. In one implementation, it is noted that themolten fuel salt 308 removed from the reactor core section 302 (shown asremoved molten fuel 312) includes at least some fissile material, whilethe feed material 310 includes at least some fertile material. Inanother implementation, the removed molten fuel 312 includes one or morefission products. For example, the removed molten fuel 312 may includewithout limitation one or more lanthanides generated via fission withinthe molten fuel salt 308. In yet another implementation, the removedmolten fuel 312 may include without limitation a mixture of fissionablematerial (e.g., UCl₄), one or more fission products (e.g., one or morelanthanides and/or a carrier salt (e.g., NaCl). While molten fuel saltexchange is described as periodic, it should be understood that suchexchange may be performed in a batch-wise, continuous, semi-continuous(e.g., drip) manner, etc.

As the molten fuel salt 308 within the reactor core section 302 breedsup, converting fertile material to fissile material, the molten fuelsalt exchange assembly 301 removes some of the molten fuel salt 308 asthe removed molten fuel 312, which contains some volume of fissilematerial, and replaces the removed molten fuel 312 with the feedmaterial 310, which includes at least some fertile material. In anotherimplementation, the removed molten fuel 312 includes one or more fissionproducts. Accordingly, the molten fuel salt exchange assembly 301 mayact as a control mechanism on the reactivity within the example MCFRsystem 300 and may serve to return the reactivity of the molten fuelsalt 308 to a critical condition (e.g., a barely critical condition).Thus, in one implementation, the molten fuel salt exchange assembly 301of the example MCFR system 300 can allow operation of the example MCFRsystem 300 indefinitely without adding further enrichment.

The molten fuel salt of the feed material 310 may include withoutlimitation one or more fertile fuel salts, such as a salt containing atleast one of depleted uranium, natural uranium, thorium, or used nuclearfuel. For example, in the case of a chloride-based fuel, one or morefertile fuel salts may include a chloride salt containing at least oneof depleted uranium, natural uranium, thorium, or a used nuclear fuel.In some cases, the feed material 310 may contain fissile fuel, such asenriched uranium, which can be fed into the example MCFR system 300 at arate or molecular volume less than the initial volume (e.g., 12.5%).This inclusion of fissile fuel in the feed fuel may be used throughoutthe lifetime of the example MCFR system 300, or alternatively, may beoccasionally used to speed up or enrich the molten fuel salt within theexample MCFR system 300 to enhance later removed fuel in future moltenfuel salt exchanges for placement in daughter reactors. Furthermore, themolten fuel salt of the feed material 310 may include without limitationone or more fissile and/or fertile fuel salts mixed with a carrier salt,such as NaCl, although other carrier salts may be employed.

The reactor core section 302 may be formed from any material suitablefor use in molten salt nuclear reactors. For example, the bulk portionof the reactor core section 302 may be formed from one or moremolybdenum alloys, one or more zirconium alloys (e.g., Zircaloy), one ormore niobium alloys, one or more nickel alloys (e.g., Hastelloy N),ceramics, high temperature steel and/or other appropriate materials. Theinternal surface of the reactor core section 302 may be coated, platedor lined with one or more additional material in order to provideresistance to corrosion and/or radiation damage. In one example, thereactor core section 302 may be constructed wholly or substantially froma corrosion and/or radiation resistant material.

In one implementation, the reactor core section 302 includes a primarycoolant system 311, which may include one or more primary coolant loops313 formed from piping 315. The primary coolant system 311 may includeany primary coolant system suitable for implementation in a molten fuelsalt context. In the illustrated implementation, the primary coolantsystem 311 circulates molten fuel salt 308 through one or more pipes 315and/or fluid transfer assemblies of the one or more of the primarycoolant loops 313 in order to transfer heat generated by the reactorcore section 302 via one or more heat exchangers 354 to downstreamthermally driven electrical generation devices and system or other heatstorage and/or uses. It should be understood that an implementation ofthe example MCFR system 300 may include multiple parallel primarycoolant loops (e.g., 2-5 parallel loops), each carrying a selectedvolume of the molten fuel salt inventory through the primary coolantsystem 311.

In the implementation illustrated in FIG. 3, the molten fuel salt 308 isused as the primary coolant. Cooling is achieved by flowing molten fuelsalt 308 heated by the ongoing chain reaction from the reactor coresection 302, and flowing cooler molten fuel salt 308 into the reactorcore section 302, at the rate maintaining the temperature of the reactorcore section 302 within its operational range. In this implementation,the primary coolant system 311 is adapted to maintain the molten fuelsalt 308 in a subcritical condition when outside of the reactor coresection 302.

It is further noted that, while not depicted in FIG. 3, the example MCFRsystem 300 may include any number of additional or intermediateheating/cooling systems and/or heat transfer circuits. Such additionalheating/cooling systems may be provided for various purposes in additionto maintaining the reactor core section 302 within its operationaltemperature range. For example, a tertiary heating system may beprovided for the reactor core section 302 and primary coolant system 311to allow a cold reactor containing solidified fuel salt to be heated toan operational temperature in which the salt is molten and flowable.

Other ancillary components may also be utilized in the primary coolantloop 313. Such ancillary components may be include one or more filtersor drop out boxes for removing particulates that precipitate from theprimary coolant during operation. To remove unwanted liquids from theprimary coolant, the ancillary components may include any suitableliquid-liquid extraction system such as one or more co-current orcounter-current mixer/settler stages, an ion exchange technology, or agas absorption system. For gas removal, the ancillary components mayinclude any suitable gas-liquid extraction technology such as a flashvaporization chamber, distillation system, or a gas stripper. Someadditional implementations of ancillary components are discussed ingreater detail below.

It is noted herein that the utilization of various metal salts, such asmetal chloride salts, in example MCFR system 300 may cause corrosionand/or radiation degradation over time. A variety of measures may betaken in order to mitigate the impact of corrosion and/or radiationdegradation on the integrity of the various salt-facing components(e.g., reactor core section 302, primary coolant piping 315, heatexchanger 354 and the like) of the example MCFR system 300 that comeinto direct or indirect contact with the fuel salt or its radiation.

In one implementation, the velocity of fuel flow through one or morecomponents of the example MCFR system 300 is limited to a selected fuelsalt velocity. For example, the one or more pumps 350 may drive themolten fuel salt 308 through the primary coolant loop 313 of the exampleMCFR system 300 at a selected fuel salt velocity. It is noted that insome instances a flow velocity below a certain level may have adetrimental impact on reactor performance, including the breedingprocess and reactor control. By way of non-limiting example, the totalfuel salt inventory in the primary loop 313 (and other portions of theprimary coolant system 311) may exceed desirable levels in the case oflower velocity limits since the cross-sectional area of thecorresponding piping of the primary loop 313 scales upward as flowvelocity is reduced in order to maintain adequate volumetric flowthrough the primary loop 313. As such, very low velocity limits (e.g., 1m/s) result in large out-of-core volumes of fuel salt and can negativelyimpact the breeding process of the example MCFR system 300 and reactorcontrol. In addition, a flow velocity above a certain level maydetrimentally impact reactor performance and longevity due to erosionand/or corrosion of the internal surfaces of the primary loop 313 and/orreactor core section 302. As such, suitable operational fuel saltvelocities may provide a balance between velocity limits required tominimize erosion/corrosion and velocity limits required to manageout-of-core fuel salt inventory. For example, in the case of a moltenchloride fuel salt, the fuel salt velocity may be controlled from 2-20m/s, such as, but not limited to, 7 m/s.

In the example implementation illustrated in FIG. 3, the molten fuelsalt exchange assembly 301 (a “molten fuel salt exchange system”)includes a used-fuel transfer unit 316 and a feed-fuel supply unit 314.In one implementation, the used-fuel transfer unit 316 includes areservoir 318 for receiving and storing used-fuel 312 (e.g., burnedfuel) from one or more portions of the MCFR system 300. As previouslynoted, the used-fuel 312 transferred to and stored in reservoir 318represents a portion of the molten fuel salt mixture 308 previously usedfission reaction within the MCFR system 300 and may include initialfissile material, bred up fissile material, fertile material and/orfission products, such as lanthanides.

In another implementation, the used-fuel transfer unit 316 includes oneor more fluid transfer elements for transferring molten fuel salt 308from one or more portions of the MCFR system 300 to the reservoir 318.The used-fuel transfer unit 316 may include any fluid transfer elementor device suitable for molten salt transfer. By way of non-limitingexample, the used-fuel transfer unit 316 may include one or more pipes320, one or more valves 322, one or more pumps (not shown) and the like.In another implementation, the used-fuel transfer unit 316 may transfermolten fuel salt 308 from any portion of the MCFR system 300 fluidicallycoupled to the reactor core section 302. By way of non-limiting example,the used-fuel transfer unit 316 may transfer molten fuel salt 308 fromany portion of the primary circuit, such as, but not limited to, thereactor core section 302, the primary coolant system 311 (e.g., primarycoolant loop 313) and the like, to the reservoir 318.

In one implementation, the feed-fuel supply unit 314 includes a feedmaterial source 317 for storing feed material 310 (e.g., mixture offertile material and carrier salt). In one implementation, the feedmaterial 310 may include a mixture of a selected fertile material (e.g.,depleted uranium, natural uranium, used nuclear fuel, thorium and thelike) and a carrier salt (e.g., NaCl) mixed such that the concentrationof the molten feed material has a concentration of fertile materialcompatible with the molten fuel salt 308 remaining in the primarycircuit of the MCFR system 300. In another implementation, the fertilematerial may include a fertile salt, such as uranium chloride, thoriumchloride and the like. In this regard, the particular components of thefeed material may be selected so as to at least approximately maintainor adjust the stoichiometry and/or chemistry (e.g., the chemicalcomposition and/or reactivity) present in the molten fuel salt 308contained within the MCFR system 300.

In one implementation, the molten fuel salt exchange assembly 301 iscapable of transferring the used fuel 312 out of the one or moreportions of the MCFR system 300 while concurrently or sequentiallytransferring the feed material (e.g., which can include a mixture of aselected fertile material and a carrier salt) into the one or moreportions of the MCFR system 300. In another implementation, thetransfers may be performed synchronously or asynchronously.

In another implementation, the feed-fuel supply unit 314 includes one ormore fluid transfer elements for transferring feed material 310 from thefeed material source 317 to one or more portions of the MCFR system 300.The feed-fuel supply unit 314 may include any fluid transfer element ordevice. By way of non-limiting example, the feed-fuel transfer unit 314may include one or more pipes 324, one or more valves 326, one or morepumps (not shown) and the like. In another implementation, the feed-fuelsupply unit 314 may transfer feed material 310 from the feed materialsource 317 to any portion of the MCFR system 300 fluidically coupled tothe reactor core section 302. By way of non-limiting example, thefeed-fuel supply unit 314 may transfer feed material 310 from the feedmaterial source 317 to any portion of the primary circuit, such as, butnot limited to, the reactor core section 302, the primary coolant system311 (e.g., primary coolant loop 315) and the like.

In one implementation, the feed material 310 is continuously transferredby the feed-fuel supply unit 314 to the reactor core section 302. By wayof non-limiting example, the feed material 310 is continuouslytransferred at a selected flow rate by the feed-fuel supply unit 314 tothe reactor core section 302. It is to be appreciated that the method ofmolten fuel salt removal may be continuous, semi-continuous, or inbatches, and may be the same as or different from the method or timingof the fuel replacement.

In another implementation, the feed material 310 is transferredbatch-wise (i.e., in discrete volume units) by the feed-fuel supply unit314 to the reactor core section 302. By way of example, the feedmaterial 310 is transferred to the reactor core section 302 at aselected frequency (or at non-regular time intervals), a selected volumetransfer size, and a selected composition for each batch transfer. Theselected frequency, volume transfer size, and composition can vary overtime.

In another implementation, the feed material 310 is transferred by thefeed-supply unit 314 to the reactor core section 302 in asemi-continuous matter. By way of non-limiting example, the feedmaterial 310 is transferred to the reactor core section 302 via dripdelivery. Such a semi-continuous feed of material (and simultaneousremoval of utilized fuel from the reactor core section 302) may allowfor limiting reactivity swings to less than 100 pcm (per cent mille orchange in k_(eff) of less than 0.01).

In another implementation, the feed-fuel supply unit 314 may includemultiple feed material sources and associated fluid transfer elements(e.g., valves and piping) to allow an exchange of multiple variations offeed materials, so as to maintain the oxidation state of the reactorcore section 302. For example, individual feed material sources, eachcontaining one of UCl₃, UCl₄, or NaCl, may be used to selectively adjustthe chemical composition of the molten fuel salt 308. See FIG. 8 for anexplanation of the ternary phase diagram for UCl₃-UCl₄-NaCl (in mole %),wherein the oxidation states and stoichiometry of the molten fuel salt308 may be controlled by adding selected volumes of UCl₃, UCl₄, or NaCl.

In one implementation, the reservoir 318 includes one or more storagereservoirs suitable for receiving and storing the molten fuel salt fromthe reactor core section 302. The reservoir 318 may be sized and ordesigned to limit reactivity of the used fuel salt 312 to reduce orlimit reactivity below criticality. The reservoir 318 may include anyone or more of neutron absorbers, moderating materials, heat transferdevices, etc. to ensure any ongoing nuclear fission reactions within theused fuel salt 312 do not exceed some specified threshold of designand/or safety. In another implementation, the reservoir 318 may includea second generation (“daughter”) fast spectrum molten salt reactor.

It should be understood that used-fuel removal and feed material supplyare coordinated to maintain the reactivity and/or composition of themolten fuel salt 308 within the reactor core section 302. Accordingly,in one implementation, the molten fuel salt exchange assembly 301includes an exchange controller 328. In one implementation, the exchangecontroller 328 may control one or more active fluid control elements inorder to control the flow of feed material 310 from the feed materialsource 317 and the flow of used fuel salt 312 from the reactor coresection 302 to the reservoir 318. In one implementation, the valves 322and 326 are active valves controllable via electronic signal from theexchange controller 328. By way of non-limiting example, the valves 322and 326 may include, but are not limited to, electronically-controlledtwo-way valves. In this regard, the exchange controller 328 may transmita control signal to one of or both of the valves 322 and 326 (or otheractive flow control mechanisms) to control the flow of feed material 310from the feed material source 317 and the flow of used fuel salt 312from the reactor core section 302 to the reservoir 318. It is notedherein that the present implementation is not limited to theelectronically controlled valves, as depicted in FIG. 3, which areprovide merely for illustrative purposes. It is recognized herein thatthere are a number of flow control devices and configurations applicableto molten salt transfer that may be implemented to control the flow offeed material 310 from the feed material source 317 and the flow of usedfuel salt 312 from the reactor core section 302 to the reservoir 318.

In one implementation, the molten fuel salt exchange assembly 301includes one or more reactivity parameter sensors 330, as discussedabove. As previously noted, the one or more reactivity parameter sensors330 may include any one or more sensors for measuring or monitoring oneor more parameters indicative of reactivity or a change in reactivity ofthe fuel salt 308 of the reactor core section 302. The reactivityparameter sensor 330 may include, but is not limited to, any one or morecapable of sensing and/or monitoring one or more of neutron fluence,neutron flux, neutron fissions, fission products, radioactive decayevents, temperature, pressure, power, isotropic concentration, burn-upand/or neutron spectrum. By way of non-limiting example, as discussedabove, the one or more reactivity parameter sensors 330 may include, butare not limited to, a fission detector (e.g., micro-pocket fissiondetector), a neutron flux monitor (e.g., a fission chamber or an ionchamber), a neutron fluence sensor (e.g., an integrating diamondsensor), a fission product sensor (e.g., a gas detector, a β detector ora γ detector) or a fission product detector configured to measure aratio of isotope types in a fission product gas. By way of anothernon-limiting example, as discussed above, the one or more reactivityparameter sensors 330 may include, but are not limited to, a temperaturesensor, a pressure sensor or a power sensor (e.g., power range nuclearinstrument).

In another implementation, the reactivity is determined with one or moreof the measured reactivity parameters (discussed above). In oneimplementation, the reactivity of the reactor core section 302 isdetermined by the controller 328 using a look-up table. In anotherimplementation, the reactivity of the reactor core section 302 isdetermined by the controller 328 using one or more models. In anotherimplementation, the reactivity parameter may be determined by anoperator and entered directly into the controller 328 via an operatorinterface. It is noted herein that, while the reactivity parametersensor 330 is depicted as being located within the fuel salt 308 in thereactor core section 302 of the MCFR system 300, this configuration isnot a limitation on the present implementation, as noted previouslyherein. In one implementation, the determined reactivity parameter(whether measured or modeled), or a parameter indicative of reactivity,is compared with a predetermined reactivity threshold. If the determinedreactivity parameter, or a parameter indicative of reactivity, satisfiesa control condition (e.g., exceeds a high threshold or falls below a lowthreshold), a control system (e.g., a molten fuel salt exchange system,a volumetric displacement system, and/or other control systems) may beactuated to adjust the reactivity of the reactor core section 302 backinto a nominal reactivity range.

In another implementation, the one or more reactivity parameter sensors330 are communicatively coupled to exchange controller 328. The one ormore reactivity parameter sensors 330 are communicatively coupled to theexchange controller 328. For example, the one or more reactivityparameter sensors 330 may be communicatively coupled to the exchangecontroller 328 via a wireline connection (e.g., electrical cable oroptical fiber) or wireless connection (e.g., RF transmission or opticaltransmission).

In one implementation, the exchange controller 328 includes one or moreprocessors and memory. In one implementation, the memory maintains oneor more sets of program instructions configured to carry out one or moreoperational steps of the molten fuel salt exchange assembly 301.

In one implementation, the one or more program instructions of theexchange controller 328, in response to the determined reactivityparameter exceeding the upper reactivity threshold, may cause theexchange controller 328 to direct the molten fuel salt exchange assembly301 to replace a selected and determined volume of the molten fuel salt308 of the MCFR system 300 with a selected and determined volume andcomposition of feed material 310 in order to control the reactivityand/or composition of the molten fuel salt 308 within the reactor coresection 302.

In another implementation, the one or more program instructions areconfigured to correlate a determined reactivity of the molten fuel salt308 of the reactor core section 302 with a selected replacement volumeand composition to compensate for the measured excess reactivity of thereactor core section 302, as well as other molten fuel saltcompositional considerations. By way of non-limiting example, thereactivity parameter sensor 330 may acquire a reactivity parameterassociated with the molten fuel salt 308 within the reactivity coresection 302 (or another portion of the MCFR system 300). In settingswhere the reactivity parameter is indicative of a reactivity larger thana selected upper threshold, the exchange controller 328 may determinethe replacement volume and composition to compensate for the elevatedreactivity and direct the molten fuel salt exchange assembly 301 toremove the determined volume of molten fuel salt 308 from the reactorcore section 302 (e.g., removed by used-fuel transfer unit 316) andreplace the removed fuel salt with a substantially equal volume of feedmaterial 310 (e.g., replaced by the feed-fuel supply unit 314).

The amount of used-fuel 312 to be removed from the reactor core section302 may be determined based upon the determined reactivity (measured ormodeled) of the reactor core section 302, the determined amount offissile and/or fertile fuel (measured or modeled), the waste (includingfission products and other possible neutron absorbers) in the moltenfuel salt 308, etc. The determined core reactivity, exceeding the upperthreshold, may be compared to a lower threshold to determine an amountof change in reactivity needed to maintain the core reactivity withinthe bounds of the selected nominal reactivity. This amount of requiredchange in reactivity can then be used with the existing fuel todetermine the amount of used-fuel 312 to be removed to maintain corereactivity within the bounds of the upper and lower thresholds ofreactivity. For example, the worth of a determined volume of removedused-fuel 312 may be determined (based upon the bum up of fissile fuel,the available fissile fuel, the remaining fertile fuel, and othercomponents, e.g., fission products and carrier salts) of the existingfuel composition, and compared if sufficient to reduce reactivity of thereactor core to the lower threshold. Based upon the determined corereactivity after fuel removal, the worth, volume and components of thefeed fuel may be determined to maintain reactivity for continuedbreeding of fuel, fuel volume requirements for the system, and maintainor adjust stoichiometry of the fuel overall. These determinations can bebased upon computational models of reactivity and reactions, look uptables based on empirical and/or modeled data, etc. As noted above, anyone or more (or combination of) the nominal reactivity level, the upperthreshold reactivity level, and/or the lower reactivity threshold maydynamically change over the lifetime of the reactor for variousoperational and/or safety reasons.

In another implementation, in settings where the frequency, volume, andcomposition of the replacement of molten fuel salt 308 with feedmaterial 310 is predetermined, the exchange controller 328 may carry outa pre-determined scheduled exchange process via the control of activeelements (e.g., valves 322 and 326, pumps and the like) of the moltenfuel salt exchange assembly 301, based on time since last exchange cycleand/or determined reactivity of the reactor core section 302, asdiscussed herein. In alternative implementations, exchange may beperformed at dynamically determined frequencies and/or volumes, based onresults from reactivity parameter sensors 330 and other sensors,monitoring techniques, and computations.

In one implementation, the selected volume and/or composition offeed-material added to the reactor core section 302 has a predetermined“worth” that can be adjusted up or down in volume and/or composition tomatch a target reactivity removal from a selected volume of used fuelremoved from the reactor core section 302.

In another implementation, the exchange controller 328 may direct themolten fuel salt exchange assembly 301 to perform a continuous exchangeof molten fuel salt 308 with feed material 310, with feed material 310being continuously fed to the reactor core section 302 and used-fuel 312being continuously removed from the reactor core section 302 at aselected rate (e.g., 0.1-10 liters/day). In another implementation, theexchange controller 328 may direct the molten fuel salt exchangeassembly 301 to perform semi-continuous exchange (e.g., drip) of moltenfuel salt 308 with feed material 310. By way of example, the exchangecontroller 328 may direct the molten fuel salt exchange assembly 301 toperform drip exchange of molten fuel salt 308 with feed material 310,with feed material 310 being drip fed to the reactor core section 302and discrete amounts of used-fuel 312 being simultaneously removed fromthe reactor core section 302. In another implementation, the exchangecontroller 328 may direct the molten fuel salt exchange assembly 301 toperform a batch-wise exchange of molten fuel salt 308 with feed material310. By way of example, the exchange controller 328 may direct themolten fuel salt exchange assembly 301 to perform a series of discrete,or batch-wise, exchanges of molten fuel salt 308 with feed material 310,with discrete amounts of feed material 310 being fed to the reactor coresection 302 and discrete amounts (equal in volume to the feed material)of used-fuel 310 being concurrently or sequentially removed from thereactor core section 302 at selected time intervals. By way of anothernon-limiting example, the exchange controller 328 may direct the moltenfuel salt exchange assembly 301 to perform a single discrete, orbatch-wise, exchange of molten fuel salt 308 with feed material 310,with a discrete amount of feed material 310 being fed to the reactorcore section 302 and an equal amount of used-fuel 312 being concurrentlyor sequentially removed from the reactor core section 302 at theselected time.

In another implementation, the MCFR system 300 includes one or more gassparging units. The one or more gas sparging units are operably coupledto the reactor core section 302 and configured to continuously removeone or more waste gases (such as gaseous fission products like noblegases) from the molten fuel salt 308 of the reactor core section 302. Byway of non-limiting example, the one or more gas sparging units includea helium and/or hydrogen gas sparging unit. It is noted that the noblegases include He, Ne, Ar, Kr and Xe. It is further noted that thegaseous waste absorbed in the molten fuel salt 308 may diffuse out ofthe molten fuel salt 308 of the reactor core section 302, allowing forthem to be pumped out of the reactor via an associated gas pump.

In another implementation, the reactor includes one or more filteringunits. The one or more filtering units are operably coupled to thereactor core section 302 and configured to continuously remove one ormore solid waste components, e.g., solid fission products such as nobleand/or semi-noble metals or other particulate waste. By way ofnon-limiting example, the one or more filtering units may include one ormore filters located in a bypass flow of the reactor core section 302arranged to collect the one or more components of the solid waste, whichprecipitate and/or plate (depending on the design geometry) out of themolten fuel salt 308. It is noted that the noble and semi-noble metalsinclude Nb, Mo, Tc, Ru, Rh, Pd, Ag, Sb and Te.

In another implementation, the primary coolant system 311 includes oneor more pumps 350. For example, one or more pumps 350 may be fluidicallycoupled to the primary coolant system 311 such that the one or morepumps 350 drive the molten fuel salt 308 through the primarycoolant/reactor core section circuit. The one or more pumps 350 mayinclude any coolant/fuel pump applicable to molten fuel salt 308. Forexample, the one or more fluid pumps 350 may include, but are notlimited to, one or more mechanical pumps fluidically coupled to theprimary coolant loop 313. By way of another example, the one or morefluid pumps 350 may include, but are not limited to, one or moreelectromagnetic (EM) and/or mechanical pumps fluidically coupled to theprimary coolant loop 313.

In another implementation, the MCFR system 300 includes a secondarycoolant system 352 thermally coupled to the primary coolant system 311via one or more heat exchangers 354. The secondary coolant system 352may include one or more secondary coolant loops 356 formed from pipes358. The secondary coolant system 352 may include any secondary coolantsystem arrangement suitable for implementation in a molten fuel saltcontext. The secondary coolant system 352 may circulate a secondarycoolant through one or more pipes 358 and/or fluid transfer assembliesof the one or more secondary coolant loops 356 in order to transfer heatgenerated by the reactor core section 302 and received via the primaryheat exchanger 354 to downstream thermally driven electrical generationdevices and systems. For purposes of simplicity, a single secondarycoolant loop 360 is depicted in FIG. 3. It is recognized herein,however, that the secondary coolant system 352 may include multipleparallel secondary coolant loops (e.g., 2-5 parallel loops), eachcarrying a selected portion of the secondary coolant through thesecondary coolant circuit. It is noted that the secondary coolant mayinclude any second coolant suitable for implementation in a molten fuelsalt context. By way of example, the secondary coolant may include, butis not limited to, liquid sodium. It is further noted that, while notdepicted in FIG. 3, the MCFR system 300 may include any number ofadditional or intermediate coolant systems and/or heat transfercircuits.

It is noted herein that the utilization of various metal salts, such asmetal chloride salts, in MCFR system 300 may cause corrosion and/orradiation degradation over time. A variety of measures may be taken inorder to mitigate the impact of corrosion and/or radiation degradationon the integrity of the various salt-facing components (e.g., reactorcore section 302, primary coolant piping 315, heat exchanger 354 and thelike) of the MCFR system 300. In one implementation, using a noble metalas a cladding for various salt-facing components can mitigate the impactof corrosion of such components. In one implementation, the use ofmolybdenum cladding on the sodium-exposed surfaces can mitigate theimpact of corrosion on such surfaces. In another implementation, themolten fuel salt may be maintained (e.g., via molten fuel salt exchange)in a redox (chemical reduction oxidation) state that is less corrosive.Certain additives may also be employed to mitigate the corrosive impactof the molten fuel salt on such components.

FIG. 4 illustrates a graph 400 of modeled k_(eff) values (curve 402) ofa reactor core and the total percentage of burn up of heavy metal (HM)fuel (curve 404) over time for a molten salt reactor controlled by theperiodic exchange of molten fuel salt of the reactor with a fertile fuelsalt. As also noted with regard to FIG. 2, the periodic exchange ofmolten fuel salt of the reactor with a fertile fuel salt may be used tolimit reactivity and maintain ongoing breed-and-burn behavior within themolten salt reactor. In another implementation, the molten fuel saltexchange assembly may feed the molten salt reactor with salt loaded withfertile material (e.g., depleted uranium) at a rate that matches therate at which fissile material is burned by the molten salt reactor, asdiscussed with regard to FIG. 5. Alternatively, the fertile material maybe added at a different rate and/or time than the fissile fuel isremoved.

FIG. 5 illustrates a graph 500 of k_(eff) (curve 502) versus time for amodeled molten salt reactor with a depleted uranium feed provided at arate that matches the reactor burn rate. It is noted that, in thisimplementation, the exchange assembly does not or need not specificallytarget lanthanides for removal from the molten salt reactor but ratherremoves them via bulk volume removal of the molten fuel salt within themolten salt reactor. The removed material may include without limitationone or more of the following: lanthanides, other fission products,fissile material, fertile material and/or the carrier salt. As shown inFIG. 5, the molten salt reactor breeds up and reaches a peak in k_(eff)of approximately 1.03 at around 10-15 years. The molten salt reactorthereafter experiences a loss in reactivity as the actinide inventory,including fissile material, falls while the fission product inventoriesincrease. It is noted that such a configuration may operate for over 20years and burn greater than 36% of the heavy metal fuel initially loadedinto the reactor and later fed to the molten salt reactor during themolten salt reactor's lifetime. Example k_(eff) ranges that may beemployed can include without limitation 1.0 as a low threshold and 1.035as a high threshold, defining an example nominal reactivity range.Another example of k_(eff) can include without limitation 1.001 as a lowthreshold and 1.005 as a high threshold, defining another examplenominal reactivity range. Yet another example nominal reactivity rangemay extend from just over 1.0 to about 1.01. Other nominal ranges andthresholds may be employed. Furthermore, other control systems may beemployed, including without limitation control rods or control drums,moderators, etc.

FIG. 6 illustrates a graph 600 depicting k_(eff) as function of time fora molten salt reactor with no addition of feed material and no removalof lanthanides. Curve 602 depicts k_(eff) for the case where wastefission products, such as noble gases and noble/semi-noble metals, areremoved from the reactor core section 302. In such a scenario,calculations indicate that 30% burn-up may be achieved, with a lifetimeof approximately 9 years. Curve 604 depicts k_(eff) as a function oftime for the cases where nothing is removed from the reactor coresection 302. In such a scenario, calculations indicate that a 10%burn-up may be achieved, with a lifetime of approximately 3 years.

FIG. 7 illustrates an alternative example MCFR system 700 equipped witha molten fuel salt exchange assembly 701. The primary coolant system isconfigured such that a primary coolant 740 includes the molten fuel saltthat circulates within the reactor vessel 742 of the reactor coresection 702 (e.g., main vessel core). In this regard, the molten fuelsalt does not flow out of the reactor core section 702 as part of theprimary coolant circuit but rather the molten fuel salt is flowed as theprimary coolant through the reactor core section 702. It is noted thatin this implementation, the MCFR system 700 may include one or more heatexchangers 746 in the primary coolant circuit for the reactor coresection 702, such that the molten fuel salt flows as the primary coolant740 through the one or more heat exchangers 746, through the reactorcore section 702, does not flow out of the reactor core section 702, andback through the one or more heat exchangers 746, as part of the primarycoolant circuit. As such, heat from the reactor core section 702 istransferred from the molten fuel salt via one or more heat exchangers746 to a secondary coolant system (not shown).

In FIG. 7, the molten fuel salt exchange assembly 701 is operablycoupled to the reactor core section 702 (or another portion of theexample MCFR system 700) and is configured to periodically replace aselected volume of the molten fuel salt 708 with a selected volume andcomposition of the feed material 710. In this regard, the molten fuelsalt exchange assembly 701 can control the reactivity and/or compositionof the molten fuel salt 708 within the example MCFR system 700. In oneimplementation, it is noted that the molten fuel salt 708 removed fromthe reactor core section 702 (shown as removed molten fuel 712 in areservoir 718) includes at least some fissile material, while the feedmaterial 710 includes at least some fertile material. In anotherimplementation, the removed molten fuel 712 includes waste that caninclude one or more fission products. For example, the removed moltenfuel 712 may include without limitation one or more lanthanidesgenerated via fission within the molten fuel salt 708. In yet anotherimplementation, the removed molten fuel 712 may include withoutlimitation a mixture of fissionable material (e.g., UCl₄), one or morefission products (e.g., one or more lanthanides and/or a carrier salt(e.g., NaCl). While molten fuel salt exchange is described as periodic,it should be understood that such exchange may be performed in abatch-wise, continuous, or semi-continuous (e.g., drip) manner and maybe periodic, sporadic or vary in timing from one fuel exchange to thenext.

In the example implementation illustrated in FIG. 7, the molten fuelsalt exchange assembly 701 (a “molten fuel salt exchange system”)includes a used-fuel transfer unit 716 and a feed-fuel supply unit 714.The molten fuel salt exchange assembly 701 may include the same orsimilar elements and operate the same or in a similar manner as themolten fuel salt exchange assembly 301 of FIG. 3, although alternativestructures and operations may also be employed. As shown in FIG. 7, anexchange controller 728 may control one or more active fluid controlelements in order to control the flow of feed material 710 from the feedmaterial source 717 and the flow of used fuel salt 712 from the reactorcore section 702 to the reservoir 718.

As the molten fuel salt 708 within the reactor core section 702 breedsup, converting fertile material to fissile material, the molten fuelsalt exchange assembly 701 removes some of the molten fuel salt 708 asthe removed molten fuel 712 in a feed material source 717, and replacesthe removed molten fuel 712 with the feed material 710, which includesat least some fertile material. In another implementation, the removedmolten fuel 712 includes one or more fission products. Accordingly, themolten fuel salt exchange assembly 701, removing not only fissile fuelbut also lanthanides and other neutron absorbers, may act as a controlmechanism on the reactivity and lifetime extender of the molten fuelsalt 708 within the example MCFR system 700. The control advantage ofthe fuel exchange may serve to return the reactivity of the molten fuelsalt 708 (monitored by a reactivity sensor 730 as discussed above withreference to reactivity sensor 330 of FIG. 3) to a critical condition(e.g., a barely critical condition) and may also increase theeffectiveness of the reactor by removing neutron absorbers and/ormodifiers. Thus, in one implementation, the molten fuel salt exchangeassembly 701 of the example MCFR system 700 can allow operation of theexample MCFR system 700 indefinitely without adding further enrichment.It should be understood that molten fuel salt exchange may occur duringoperation of the nuclear reactor and/or during maintenance shut-downperiods.

The molten fuel salt of the feed material 710 may include withoutlimitation one or more fertile fuel salts, such as a salt containing atleast one of depleted uranium, natural uranium, thorium, or used nuclearfuel. For example, in the case of a chloride-based fuel, one or morefertile fuel salts may include a chloride salt containing at least oneof depleted uranium, natural uranium, thorium, or a used nuclear fuel.Furthermore, the molten fuel salt of the feed material 710 may includewithout limitation one or more fertile fuel salts mixed with a carriersalt, such as NaCl, although other carrier salts may be employed.

FIG. 8 illustrates an example ternary phase diagram 800 forUCl₃-UCl₄-NaCl (in mole %). In one implementation, an MCFR system, asmodelled, uses a salt mixture composed of various sodium chloride anduranium chloride components. One example of such compositions mayinclude one more components of NaCl, UCl₃, and/or UCl₄, as shown in theternary phase diagram 800 of FIG. 8. The shaded region 802 shows theextent of a 500° C. melting point envelope. Multiple fuel saltcompositions have been considered and have been shown to be capable ofnet breed and burn behavior. Selection of the final composition dependson a variety of factors including oxidation state/corrosion, solubility,viscosity and reactor size.

Modelling has investigated different specific salts in the ternarydiagram 800 with melting points suitable for use in the MCFRimplementations, including without limitation82UCl₄-18UCl_(3, 17)UCl₃-71UCl₄-12NaCl, and 50UCl₄-50NaCl. Results ofthe modelling indicate that such fuel salt implementations will sustainbreed and burn behavior and could be used in reactor implementationsdescribed herein.

As mentioned, the ternary phase diagram 800 shows the expected meltingtemperature for any mixture of UCl₃-UCl₄-NaCl. Of particular interestare mixtures having a melting point less than about 500° C., whichmixtures are illustrated in the shaded region 802 of the ternary phasediagram 800. The eutectic point 804 has a melt temperature of 338° C.and a composition of 17UCl3-40.5UCl4-42.5NaCl (i.e., 17 mol % UCL3, 40.5mol % UCL4 and 42.5 mol % NaCl). The shaded region 802 indicates amelting point envelope of 500° C. Moving to the far-right of this shadedregion 802 provides an example implementation 806, 17UCl3-71UCl4-12NaCl,but it should be understood that many possible compositions exist withinthe melting point envelope of the shaded area 802 as various fuel saltmixtures having a melting point below 500° C. Furthermore, if themelting temperature limit is slightly extended to 508° C., a compositionof 34UCl3-66NaCl provides an option that is free of UCl₄. Likewise, theternary diagram 800 allows a range of specific UCl3-UCl4-NaCl fuel saltimplementations to be identified for any given melting point limitbetween about 800° C. and 338° C. For example, ternary salts withmelting points between 300-550° C., 338-500° C., and 338-450° C. may beeasily identified. Example methods of detecting composition changes mayinclude without limitation:

-   -   1) measurements of redox (chemical reduction oxidation)    -   2) online glow discharge mass spectrometry of a sample    -   3) reactivity changes in the core    -   4) offline sample analysis including GDMS (glass discharge mass        spectroscopy)    -   5) gamma spectroscopy

The specific composition of the mixture may include any formulationincluding two or more of UCl₄, UCl₃ or NaCl, such that the resultinguranium content level and melting temperature achieve desired levels. Byway of non-limiting example, the specific composition may be selected sothat the corresponding melting temperature falls between 330 and 800° C.By way of another non-limiting example, the specific composition may beselected so that the overall uranium content level is at or above 61% byweight. In addition to selecting the overall uranium content level thefuel composition may also be determined to meet a selected amount offissile uranium (as opposed to fertile). For example, the specificcomposition of the molten fuel salt may be selected such that the U-235content of the molten fuel salt is below 20%.

The following discussion will identify particular implementations ofinterest, however the following discussion does not limit the scope ofthe invention as claimed to only the implementations described below,but rather, that any implementations identifiable from FIG. 8 arecontemplated, as well as any implementations having different metalchlorides other than NaCl. Examples of additional, non-fissile metalchlorides include NaCl, MgCl₂, CaCl₂, BaCl₂, KCl, SrCl₂, VCl₃, CrCl₃,TiCl₄, ZrCl₄, ThCl₄, AcCl₃, NpCl₄, PuCl₃, AmCl₃, LaCl₃, CeCl₃, PrCl₃and/or NdCl₃.

Liquid fuels have an inherent advantage over solid fuels in that theheat is “born” within the fuel coolant. A solid fuel may (1) conductheat to the outer surface of the fuel element, (2) conduct heat throughthe cladding (including past a physical gap or through a bond material),(3) convect the heat from the cladding surface to the primary coolant,and (4) advect the heat out of the core. By comparison, a liquid fuelprovides acceptable thermal transfer with step (4) and transport thefuel salt/primary coolant out of the core and to the primary heatexchanger. Additionally, the liquid salts under consideration havevolumetric heat capacities that are nearly twice that of liquid sodiumat similar temperatures.

Another key advantage provided by a molten fuel salt is the strongnegative temperature coefficient—hot salt is less reactive than coldsalt. As a result, transients that result in overheating (e.g., loss ofheat sink) are limited in severity by the expansion of the fuel salt.For example, in a molten chloride fast reactor (MCFR), as the selectedchloride salt composition is heated from 600 to 800° C., its densitydrops by more than 12%, providing a negative reactivity feedback that isapproximately 50× stronger than that provided by the Doppler effect.

Fuel salts with similar ratios of the number of mono-chlorides,tri-chlorides, and tetra-chlorides behave similarly. The oxidation statewithin reactor core section of a molten chloride fast reactor (MCFR),for example, may be defined as the ratio of the molecules grouped by thenumber of attached chlorine molecules. The oxidation state of thereactor core section can be controlled by exchanging a selected amountof fuel salt in the reactor core section with a similar amount of makeupsalt or feed material, where the composition of the feed material isdesigned to bring the oxidation state of the reactor core section towarda target oxidation state. In one implementation, the feed materialcontains a mixture of a selected fertile material and a carrier salt.

In one implementation, the fuel salt in the reactor core section isinitially at an oxidation state that is mostly composed ofmono-chlorides, tri-chlorides, and tetra-chlorides. This initial fuelsalt composition (prior to removal a selected volume of the fuel saltand addition of feed material) is represented by the initial fuel saltvector (f), where the subscript x represents the number of chloride ionspresent in each molecule of the fuel salt. Molecules with 2, 5 and 6chloride atoms can exist within the reactor core section in very smallquantities, so they can be ignored—the bulk properties of the moltenchloride fuel are dominated by the mono-chlorides, tri-chlorides, andtetra-chlorides (see Equation (1), which indicates a simplified fuelsalt vector in which the molten chloride fuel is dominated bymono-chlorides (f₁), tri-chlorides (f₃), and tetra-chlorides (f₄)). Assuch, if the target salt mixture is PbCl₂-UCl₃-UCl₄ (orPuCl₂-UCl₃-UCl₄), one would control on di-chlorides, tri-chlorides, andtetra-chlorides. Note: the fuel salt vector may be generalized to otherchloride salts and fluoride salts. Accordingly, a similar controlapproach may be applied to fluoride salts, where the subscript xrepresents the number of fluoride ions in each molecule of the fuelsalt.

$\begin{matrix}{{\begin{pmatrix}f_{1} \\f_{2} \\f_{3} \\f_{4} \\f_{5} \\f_{6}\end{pmatrix}\text{∼}\begin{pmatrix}f_{1} \\f_{3} \\f_{4}\end{pmatrix}} = (f)} & (1)\end{matrix}$

As such, the initial fuel salt vector (f) may be represented by thesimplified fuel salt vector given in Equation (1).

Removal of a selected volume (r) of the initial fuel salt over a periodof time (either as a large batch, a set or sequence of smaller batches,or a continuous or partially continuous stream) normalized to the amountof initial fuel salt present in the reactor at the start of that periodof time (e.g., about 1% per year for a specific MCFR system) yields anadjusted fuel salt vector (f), which is shown by Equation (2),representing the fuel salt remaining in the reactor after removal of aselected volume of the initial fuel salt.

$\begin{matrix}{\left. {\begin{pmatrix}f_{1} \\f_{3} \\f_{4}\end{pmatrix}\text{∼}C*\begin{pmatrix}f_{1} \\f_{3} \\f_{4}\end{pmatrix}}\rightarrow\begin{pmatrix}{f^{\prime}}_{1} \\{f^{\prime}}_{3} \\{f^{\prime}}_{4}\end{pmatrix} \right. = \left( f^{\prime} \right)} & (2)\end{matrix}$

A target fuel salt composition within the reactor, represented by atarget fuel salt vector (t), may be set to achieve a particularoxidation state and/or stoichiometry from the adjusted fuel saltcomposition (adjusted fuel salt composition (f) by adding a selectedvolume and composition of feed material, which is represented by a feedfuel salt vector (m). This relationship is represented by Equations (3)and (4), where (r)˜C*(f).

(f)−(r)=(f′)  (3)

(f′)+(m)=(t)  (4)

In an alternative notation, this relationship is represented byEquations (5) and (6).

$\begin{matrix}{{\begin{pmatrix}f_{1} \\f_{3} \\f_{4}\end{pmatrix} - \begin{pmatrix}r_{1} \\r_{3} \\r_{4}\end{pmatrix}} = \begin{pmatrix}{f^{\prime}}_{1} \\{f^{\prime}}_{3} \\{f^{\prime}}_{4}\end{pmatrix}} & (5) \\{{\begin{pmatrix}{f^{\prime}}_{1} \\{f^{\prime}}_{3} \\{f^{\prime}}_{4}\end{pmatrix} + \begin{pmatrix}m_{1} \\m_{3} \\m_{4}\end{pmatrix}} = \begin{pmatrix}t_{1} \\t_{3} \\t_{4}\end{pmatrix}} & (6)\end{matrix}$

Given Equations (3)-(6), the volume and composition of the feed materialto be added to the reactor to achieved the target oxidation state and/orstoichiometry may be determined (e.g., (m)). For each molecule type, themakeup fuel salt vector (m_(x)) may be represented by Equation (7),where the subscript x represents the number of fluoride ions in eachmolecule of the fuel salt and C represents the normalized amount removedin a given period of time.

(m _(x))=(t _(x))−(1−C)*(f _(x))  (7)

Nuclear fission reactors operate at zero or approximately zero excessreactivity to operate at a constant power. In addition to controllingthe oxidation state of the molten fuel salt in the reactor, thereactivity of the described molten salt reactor implementations can beadjusted in situ by swapping fuel salt for a feed material.

In a burner molten salt reactor, fissile material is burned soreactivity tends to decrease with time. As such, the feed material isdesigned to contain a significant quantity of high reactivity fuel saltrich in fissile material, such as enriched uranium or reprocessedtransuranics. In a breeder molten salt reactor, fissile material isproduced faster than it is consumed by the fission reaction, so thereactivity tends to increase with time. As such, the feed material isdesigned to contain low reactivity fuel salt that is rich in fertilematerial, such as natural uranium, depleted uranium, used nuclear fuel,or thorium. The rate at which feed material is introduced to the reactorcore is selected to maintain the reactivity within certain designlimits, such as nominal reactivity (e.g. k_(eff) equaling 1 or slightlygreater than 1, an upper reactivity threshold, and/or a lower reactivitythreshold).

FIG. 9 illustrates example operations 900 for a molten fuel saltexchange process. A system provisioning operation 902 provides a moltenchloride fast reactor (which is an example molten salt reactor) with amolten fuel salt exchange system. A monitoring operation 904 monitorsfor an exchange condition for the molten fuel salt. For example, one ormore reactivity parameter sensors may monitor the reactivity within themolten chloride fast reactor, and/or chemical composition sensors, suchas Raman spectroscopy may monitor the composition of the molten fuelsalt within the molten chloride fast reactor. In an implementation, themonitoring may be performed in real-time using Raman spectroscopy. Ramanspectroscopy provides information about molecular vibrations that can beused for sample identification and quantitation. The technique involvesshining a monochromatic light source (i.e. laser) on a sample anddetecting the scattered light. Some amount of fuel may be removed fromthe reactor core, such as in a side stream, and passed through amonitoring cell that includes a ‘window’ through with the spectroscopycan be performed. Examples of Raman windows materials are fused quartz,fused silica, sapphire, diamond, and some glasses. Any material may beused as long as it can meet the operational parameters of the reactorand monitoring system. An exchange condition may be set for monitoredreactivity, composition, or some other operating parameter to trigger amolten fuel salt exchange event.

If the exchange condition has not been satisfied, then a decisionoperation 906 returns processing to the monitoring operation 904. If theexchange condition has been satisfied, then the decision operation 906progresses processing to a removal operation 908, which removes aselected volume of molten fuel salt from the molten chloride fastreactor. A replacement operation 910 replaces the removed volume of themolten fuel salt with a selected volume and/or composition of feedmaterial into the molten chloride fast reactor. Processing returns tothe monitoring operation 904.

FIG. 10 illustrates a molten salt reactor 1000 equipped with avolumetric displacement element assembly 1002. Volumetric displacementsystems represent a type of molten fuel salt control system. In oneimplementation, the volumetric displacement assembly 1002 is operablycoupled to the reactor core section 1004 containing a molten fuel salt1006. The volumetric displacement assembly 1002 is arranged so as toselectively displace a volume of the molten fuel salt 1006. In thisregard, the volumetric displacement assembly 1002 may displace a volumeof the fuel salt 108 in order to control reactivity within the moltenfuel salt 1006. The volumetric displacement element assembly 1002 maycontrol reactivity of the molten salt reactor 1000 by controlling thevolume of molten fuel salt 1006, and thus the fissile material,displaced in the reactor core section 1004 (e.g., center region of thecore section). By way of a non-limiting example, in settings where thereactor core section 1004 possesses excess reactivity, a sufficientvolume (e.g., 0.1 to 10.0 m³) of molten fuel salt 1006 may be displacedby the volumetric displacement assembly 1002 such that the reactivitydecreases to a lower reactivity threshold, such as critical orsub-critical levels. It should be appreciated that multiple volumetricdisplacement assemblies may be used in various configurations within themolten salt reactor 1000.

In one implementation, the volumetric displacement assembly 1002includes a volumetric displacement element 1010, an actuator 1012 and anactuator controller 206. In one implementation, the volumetricdisplacement element 1010 is formed from a non-neutron-absorbingmaterial. In this regard, the volumetric displacement element 1010controls reactivity in the molten salt reactor 1000 via the volumetricfluid displacement of the molten fuel salt 1006 (and fissile material)and not through a neutron absorption process. It is noted that theutilization of a non-neutron-absorbing material is particularlyadvantageous in the molten salt reactor 1000 as it avoids large impactson reactivity, which may occur with the introduction ofneutron-absorbing materials into the reactor core section 1004. Anon-neutron-absorbing volumetric displacement element, which operatesbased on volumetric fluid displacement of the molten salt, may providesubtler reactivity control than neutron-absorbing control elements.

It should be understood, however, that the volumetric displacementelement 1010 (e.g., displacement rod) may be formed from any non-neutronabsorbing material, although neutron absorbing and/or moderatingmaterials may additionally or alternatively be employed in suchelements. As such, the volumetric displacement element 1010 mayalternatively include a neutron transparent material or a neutronreflector material. For example, the volumetric displacement element1010 may be formed, but is not required to be formed, from zirconium,steel, iron, graphite, beryllium, molybdenum, lead, tungsten, boron,cadmium, one or more molybdenum alloys (e.g., TZM alloy), one or moretungsten alloys (e.g., tungsten carbide), one or more tantalum alloys,one or more niobium alloys, one or more rhenium alloys, one or morenickel alloys, silicon carbide and the like. In such implementations,the volumetric displacement element 1010 may limit reactivity throughthe volumetric fluid displacement of fuel and through the absorption ofneutrons.

In one implementation, the volumetric displacement element 1010 includesa rod 1016, as shown in FIG. 10. For example, the volumetricdisplacement element 1010 includes a solid rod or a hollow rod. It isnoted herein that the displacement rod 1016 may take on any type of rodshape. For example, a displacement rod of the volumetric displacementassembly 1010 may take on a cylindrical shape, a square or rectangularprism shape, a triangular prism shape, a polygonal prism shape and thelike. In another implementation, the volumetric displacement element1010 may include a set of rods (not shown). For example, the set of rodsmay be arranged in an array or spoke pattern.

In one implementation, the actuator 1012 is operably coupled to thevolumetric displacement element 1010, such that the actuator 1012 mayselectively translate the volumetric displacement element 1012. Theactuator 1012 may include any actuation device. For example, theactuator 1012 may include, but is not limited to, a displacement roddrive mechanism. In one implementation, the actuator 1012 is configuredto drive the volumetric displacement element 1010 bidirectionally. Inthis regard, the actuator 1012 may drive the volumetric displacementelement 1010 into and/or out of the reactor core section 1004 asdesired. In another implementation, the actuator 1012 is configured tostop driving the volumetric displacement element 1010 at one or moreintermediate positions between a first stop position and a second stopposition. In this regard, the actuator 1012 may translate the volumetricdisplacement element 1010 along a selected direction (e.g., axialdirection) so as to insert a selected amount of the volumetricdisplacement element 1010 into the molten fuel salt 1006 of the reactorcore section 1004. For example, in the case of a rod-shaped volumetricdisplacement element 1010, the actuator 1012 may insert a selectedvolume of the volumetric displacement element 1010 by controlling thelength L of the rod-shaped volumetric displacement element 1010 insertedinto the molten fuel salt 1006.

It is noted that the volumetric displacement assembly 1002 may displaceany amount of volume of the molten fuel salt 1006 within the reactorcore section 1004 necessary to reduce the reactivity of the molten fuelsalt 1006 within the reactor core section 1004 as desired. By way ofnon-limiting example, the volume of molten fuel salt 1006 within thereactor core section 1004 may range from 10 to 100 m³, depending on theparticular fuel formulation and operation context of the molten saltreactor 1000. In this setting, a displacement volume of only a fractionof a cubic meter may supply sufficient volumetric salt displacement tosignificantly reduce reactivity within the reactor core section 1004and, in some cases, shutdown the reactor. For example, in marginalcontrol or non-shutdown operations, the displacement volume imparted bythe volumetric displacement element 1010 may include, but is not limitedto, a displacement volume between 0.1 to 10 m³.

In one implementation, as shown in FIG. 10, the volumetric displacementassembly 1010 may insert the volumetric displacement element 1010 into acentral region of the reactor core section 1004. In this regard, theactuator 1012 may translate the volumetric displacement element 1010along the axial direction of the reactor core section 1004, as shown inFIG. 10. It is noted that given a rotationally symmetric core section,as that depicted in FIG. 10, the greatest reactivity worth associatedwith the volumetric displacement element 1010 may be realized bypositioning the volumetric displacement element 1010 at thecross-sectional center of the reactor core section 1004. It is notedthat a centered volumetric displacement element 1010 is not a limitationon the molten salt reactor 1000 of the present disclosure and isprovided merely for illustrative purposes. Moreover, althoughdisplacement element 1010 is shown in FIG. 10 as a single element, it isto be appreciated that the displacement element may include a pluralityof insertable elements, which may move into and out of the reactor corein tandem or may be moved and controlled individually to managereactivity, fuel flow, local temperature, etc.

In another implementation, the actuator controller 1010 is configured toselectively direct the actuator 1012 to insert a selected volume of thevolumetric displacement element 1010 a selected distance into a volumeof the molten fuel salt 1006 contained within the reactor core section1004. For example, the actuator controller 1014 may direct the actuator1012 to translate the volumetric displacement element 1010 such that thevolumetric displacement element 1010 partially or entirely submerses inthe molten fuel salt 1006. The actuator controller 1014 iscommunicatively coupled to the actuator 1012. For example, the actuatorcontroller 1014 may be communicatively coupled to the actuator 1012 viaa wireline connection (e.g., electrical cable or optical fiber) orwireless connection (e.g., RF transmission or optical transmission).

In one implementation, the actuator controller 1012 includes an operatorinterface configured to receive volumetric displacement actuationinstructions from an operator. In this regard, an operator mayselectively direct the control the actuation state of the volumetricdisplacement element 1010. In another implementation, the actuationcontroller 1014 may automatically direct the actuation of the volumetricdisplacement element 1010 in response to one or more sensed or monitoredparameters of the molten salt reactor 1000, as discussed below.

In another implementation, the molten salt reactor 1000 includes areactivity parameter sensor 1030. The reactivity parameter sensor 1030includes any one or more sensors capable of measuring or monitoring oneor more parameters indicative of reactivity or a change in reactivity ofthe molten fuel salt 1006 of the molten salt reactor 1000. For example,the reactivity parameter sensor 1030 may include, but is not limited to,any one or more sensors capable of sensing and/or monitoring one or moreof neutron fluence, neutron flux, neutron fissions, fission products,radioactive decay events, temperature, pressure, power, isotropicconcentration, burn-up and/or neutron spectrum.

In one implementation, the reactivity parameter sensor 1030 includes afission detector. For example, the reactivity parameter sensor 1030 mayinclude, but is not limited to, a micro-pocket fission detector. Inanother implementation, the reactivity parameter sensor 1030 includes aneutron flux monitor. For example, the reactivity parameter sensor 1030may include, but is not limited to, a fission chamber or an ion chamber.In another implementation, the reactivity parameter sensor 1030 includesa neutron fluence sensor. For example, the reactivity parameter sensor1030 may include, but is not limited to, an integrating diamond sensor.In another implementation, the reactivity parameter sensor 1030 includesa fission product sensor. For example, the reactivity parameter sensor1030 may include, but is not limited to, a gas detector, a β detector ora γ detector. In another implementation, the reactivity parameter sensor1030 includes a fission product detector configured to measure a ratioof isotope types in a fission product gas.

In another implementation, the reactivity parameter sensor 1030 includesa temperature sensor. In another implementation, the reactivityparameter sensor 1030 includes a pressure sensor. In another example,the reactivity parameter sensor 1030 includes a power sensor. Forexample, the reactivity parameter sensor 1030 may include, but is notlimited to, a power range nuclear instrument.

In another implementation, the reactivity is determined with one or moreof the measured reactivity parameters (discussed above). In oneimplementation, the reactivity of the reactor core section 1004 isdetermined by the actuator controller 1012 using a look-up table. Forexample, measured values for temperature, pressure, power level and thelike may be used in conjunction with one or more look up tables todetermine the reactivity of the reactor core section 1004. In anotherimplementation, the reactivity of the reactor core section 1004 isdetermined by the actuator controller 1014 using one or more models. Forexample, the one or more models may include, but are not limited to, aneutronics modeling software package executed by the one or moreprocessors of the actuator controller 1014. For instance, a suitableneutronics software package may include, but is not limited to, MCNP,CINDER, REBUS and the like. In another implementation, the reactivityparameter may be determined by an operator and entered directly into theactuator controller 1014 via an operator interface.

It is noted herein that, while the reactivity parameter sensor 1030 isdepicted as being located within the molten fuel salt 1006 in thereactor core section 1004 of the molten salt reactor 1000, thisconfiguration is not a limitation on the present implementation and isprovided merely for illustrative purposes. Rather, it is noted that oneor more reactivity parameter sensors 1030 may be located at variouspositions of the molten salt reactor 1000 including, but not limited to,at a position within the reactor core section, at a position external tothe reactor core section 1004 (e.g., at external surface of reactor coresection 1004), in or along one or more pipes of a primary coolantsystem, in or near a primary heat exchanger, in or along one or morepipes of a secondary coolant system and the like.

In another implementation, the one or more reactivity parameter sensors1030 are communicatively coupled to actuator controller 1014. The one ormore reactivity parameter sensors 1030 are communicatively coupled tothe actuator controller 1014. For example, the one or more reactivityparameter sensors 1030 may be communicatively coupled to the actuatorcontroller 1014 via a wireline connection (e.g., electrical cable oroptical fiber) or wireless connection (e.g., RF transmission or opticaltransmission).

In one implementation, the actuation controller 1014 may direct theactuator 1012 to adjust the position of the volumetric displacementelement 1010 (and, thus, the reactivity of the molten fuel salt 1006)based on the measured reactivity parameter.

In one implementation, the actuation controller 1014 includes one ormore processing units and memory. In one implementation, the memorymaintains one or more sets of program instructions configured to carryout one or more operational steps of the volumetric displacementassembly 1010. In one implementation, the one or more programinstructions of the actuation controller 1014 may cause the actuatorcontroller 1014 to direct the actuator 1012 to drive the volumetricdisplacement assembly 1010 into the reactor core section 1004 todisplace a selected volume of the molten fuel salt 1006 within thereactor core section 1004.

In another implementation, the one or more program instructions areconfigured to correlate a determined reactivity of the reactor coresection 1004 with a displacement volume necessary to compensate for themeasured reactivity of the reactor core section 1004. For example, asdiscussed above, the reactivity parameter sensor 1030 may acquire areactivity parameter associated with the molten fuel salt 1006 withinthe reactivity core section 1004. In settings where the reactivityparameter is indicative of a reactivity larger than a selected tolerancelevel, the actuator controller 1014 may determine the displacementvolume to compensate for the elevated reactivity and direct the actuator1012 to insert enough of the volumetric displacement element 1010 toachieve at least this level of volumetric salt displacement. In anotherimplementation, in settings where complete reactor shutdown is required,the actuator controller 1014 may direct the actuator 1012 to insert theentire volumetric displacement element 1010 into the reactor coresection 1004 in order to achieve maximum volumetric salt displacement.

FIG. 11 illustrates a molten salt reactor 1100 equipped with avolumetric displacement element assembly 1102 and a molten fuel saltspill-over system 1130 with a volumetric displacement element 1110 notsubmerged in molten fuel salt. In one implementation, the molten fuelsalt spill-over system 1130 includes one or more fuel salt uptakes 1132and one or more spill-over reservoirs 1134. It is noted that in somecases the volumetric displacement of the molten fuel salt 1106 by thevolumetric displacement element 1110 may cause a rise in the fuel saltlevel above a desired level. In one implementation, the molten fuel saltspill-over system 1130 is configured to transport molten fuel salt 1106that is displaced above the maximum tolerated fill level of the reactorcore section 1104, as shown in FIG. 12. By way of non-limiting example,the fuel salt uptake 1132 may be placed approximately 10 cm above anominal fuel salt level. In this regard, when the volumetricdisplacement element 1110 is engaged, it may, in some cases, cause themolten fuel salt level to rise above normal salt level. Molten salt thatreaches the fuel salt uptake 1132 is then transported to the spill-overreservoir 1134. It should be appreciated that multiple volumetricdisplacement assemblies may be used in various configurations within themolten salt reactor 1100.

FIG. 12 illustrates a molten salt reactor 1200 equipped with avolumetric displacement element assembly 1202 and a molten fuel saltspill-over system 1230 with a volumetric displacement element 1210submerged in molten fuel salt. While the molten fuel salt spill-oversystem 1230 depicted of FIG. 12 is depicted in the context of thevolumetric displacement element assembly 1202 and volumetricdisplacement element 1210, this is not a requirement on the molten fuelsalt spill-over system 1230. In this regard, the molten fuel saltspill-over system 1230 of the present disclosure may be implemented in acontext that does not include the volumetric displacement assembly 1202and volumetric displacement element 1202. In one implementation, themolten fuel salt spill-over system 1230 may be implemented in order toaccount for thermal expansion of the molten fuel salt 1206. By way ofnon-limiting example, in the case where the fuel salt uptake 1232 isplace at 10 cm above the normal salt level a mere 50° C. increase intemperature of the fuel salt 108 may cause the molten fuel salt 1206 toreach the fuel salt uptake 1232. By way of another non-limiting example,approximate increase of 200° C. in temperature of the molten fuel salt1206 may cause the molten fuel salt 1206 to spill over through the fuelsalt uptake 1232 and lead to 1-5 m³ of fuel salt to spill into one ormore spill-over reservoirs 1234. Spilled-over fuel salt 1236 is shown inthe one or more spill-over reservoirs 1234.

It is recognized herein that the combination of very low excessreactivity and the strong thermal feedback of the molten fuel salt 1206may allow for nearly passive operation. In this sense, use of thedisplacement element 1210 may be limited. As the demand on the turbine(not shown) of the nuclear reactor plant varies, the temperature(s)associated with the primary cooling loop will vary slightly. This, inturn, will vary the temperature of the molten fuel salt 1206. As aresult, the molten fuel salt 1206 will obtain a new average temperature,and thus, density, causing the fluid level of the molten fuel salt 1206to increase or decrease.

By way of non-limiting example, in the event that demand for electricityincrease, the steam of the turbine comes out at a reduced temperature.As a result, temperatures throughout the nuclear reactor system arereduced, causing the molten fuel salt 1206 to decrease in temperatureand increase in density. This increase in density results in an increasein reactivity. In addition, the fluid level of the molten fuel salt 1206is decreases, while increased reactivity causes the power of the moltensalt reactor 1200 to increase, thereby meeting the increased demand onthe turbine. In turn, increase in power causes the temperature of themolten fuel salt 1206 to increase and the fluid level of the molten fuelsalt 1206 to return to (or near) its original level.

It is further recognized that, in the event of a loss of heat sink or aturbine trip, temperatures throughout the molten salt reactor 1200 wouldincrease. As a result of increased temperatures in the molten fuel salt1206, the molten fuel salt 1206 would decrease in density, causing themolten fuel salt 1206 to become less reactive. The decrease in densitywould cause the fluid level to rise and, in some instances (e.g., +50°C. temperature rise) the fluid level of the molten fuel salt 1206 reachthe level of the fuel salt uptake 208. Such a rise in fluid level maythen cause some molten fuel salt 1206 to spill over into the one or morespill-over reservoirs 1234, which would serve to further reducereactivity in the reactor core section 1204. As a result, the moltensalt reactor 1200 may go into a sub-critical state and remain in thatstate, even upon cooling. In another implementation, the molten fuelsalt spill-over system 1230 may include a return pathway (e.g., one ormore pipes, one or more pumps and one or more valves), where fuel saltstored in the one or more spill-over reservoirs 1234 may be activelypumped out of the one or more spill-over reservoirs 1234 and back intothe reactor core section 1204 in order to reestablish a critical state.

In another implementation, the displacement element 1210 may be used toaccelerate the above process as well as control or shape changes inreactivity/density/temperature during normal operation. It should alsobe understood that various structural modifications to the displacementelement 1210 may be employed to enhance control performance and manageinfluence that molten fuel salt turbulence may have on the placement andstability of the displacement element 1210 within the reactor coresection 1204. Such structural modifications may include withoutlimitation different shapes, sizes, and numbers of displacement elements1210, dynamic shape change features in displacement element 1210,baffles and/or nozzles in the displacement element 1210, and otherflow-friendly features to the displacement element 1210. It should beappreciated that multiple volumetric displacement assemblies may be usedin various configurations within the reactor core section 1204.

FIG. 13 illustrates various example stages of a fuel displacement cycle1300. In stage 1302, the displacement element 1301 includes a hollow orsolid displacement rod 1303 inserted through rod inlet 1305 and adisplacement body 1307 having a width w that is wider than both thedisplacement rod 1303 and the rod inlet 1305 and a height h that is lessthan the height y of the reactor core section 1311. As a result, themaximum volume of displacement can be vertically selected/located withinthe reactor core section 1311 by raising or lowering the displacementbody 1307 to a desired height in the molten fuel salt 1309 within thereactor core section 1311. The dashed line 1320 indicates the moltenfuel salt level when the displacement element has not yet been loweredinto the molten fuel salt 1309.

It should be understood that the displacement rod 1303 and/or thedisplacement body 1307 may be formed of or filled with variousmaterials, including non-neutron absorbing materials and neutronabsorbing materials.

In stage 1302, the displacement element has been partially lowered intothe molten fuel salt, resulting in a raising of the molten fuel saltlevel. The subsequent stages 1304, 1306, 1308, 1310, and 1312 showprogressively lower insertions of the displacement body 1307 into themolten fuel salt 1309, resulting in increasingly higher levels of themolten fuel salt 1309, although such increasing levels of molten fuelsalt 1309 may be mitigated by a spill-over system. Stage 1312illustrates a fully immersed displacement body 1307.

By displacing the volume of molten fuel salt 1309 at a particularlocation within the reactor core section, the reactivity within thereactor core section 1311 can be controlled. Even after the displacementbody 1307 is fully immersed within the molten fuel salt 1309, thevertical location within the reactor core section 1311 can furtherinfluence the reactivity (e.g., the lower the displacement body 1307,the more negative influence on reactivity) in the illustratedimplementations. See FIG. 14 and the associated discussion.

It should be appreciated that multiple volumetric displacementassemblies may be used in various configurations within the reactor coresection 1311.

FIG. 14 illustrates two example stages 1402 and 1404 of a fueldisplacement cycle 1400. In stage 1402, the displacement element 1401includes a hollow or solid displacement rod 1403 and a displacement body1407 inserted deep into molten fuel salt 1409 within a reactor coresection 1411. In stage 1404, the displacement body 1407 inserted lessdeeply into the molten fuel salt 1409 within the reactor core section1411. As a result, the maximum volume of displacement can be verticallyselected/located within the reactor core section 1411 by raising orlowering the displacement body 1407 to a desired height in the moltenfuel salt 1409 within the reactor core section 1411. It should beunderstood that the displacement rod 1403 and/or the displacement body1407 may be formed of or filled with various materials, includingnon-neutron absorbing materials and neutron absorbing materials.Accordingly, in one implementation, the reactivity control may becharacterized as more negative in the stage 1402 than in the stage 1404because the displacement body 1407 is inserted more deeply into thereactor core section 1411, displaying more fuel at an input region ofthe reactor core section 1411, where the molten fuel salt 1409 firstenters the active fission reaction region at each circulation cycle.

It should be appreciated that multiple volumetric displacementassemblies may be used in various configurations within the reactor coresection 1411.

FIG. 15 illustrates example operations 1500 for a molten fuel saltdisplacement process. A system provisioning operation 1502 provides amolten chloride fast reactor (which is an example molten salt reactor)with a molten fuel salt exchange system. A monitoring operation 1504monitors for a control condition for the molten fuel salt (e.g.,k-effective meets or exceeds a threshold, such as 1.005). For example,one or more reactivity parameter sensors may monitor the reactivitywithin the molten chloride fast reactor. The control condition may beset for monitored reactivity or some other operating parameter totrigger a molten fuel salt displacement event.

If the control condition has not been satisfied, then a decisionoperation 1506 returns processing to the monitoring operation 1504. Ifthe control condition has been satisfied, then the decision operation1506 progresses processing to an insertion operation 1508, which insertsa displacement body into molten fuel salt within a reactor core section.A positioning operation 1510 positions the displacement body into themolten fuel salt of the molten chloride fast reactor to remove aselected volume of molten fuel salt from the reactor core section toobtain desired reactivity parameters in the molten chloride fastreactor. Processing returns to the monitoring operation 1504.

In one implementation, an example molten salt reactor includes a nuclearreactor core configured to contain a nuclear fission reaction fueled bya molten fuel salt. A molten fuel salt control system is coupled to thenuclear reactor core and is configured to remove a selected volume ofthe molten fuel salt from the nuclear reactor core to maintain aparameter indicative of reactivity of the molten salt reactor within aselected range of nominal reactivity.

Another example molten salt reactor of any preceding reactor provides amolten fuel salt control system that includes a molten fuel saltexchange system fluidically coupled to the nuclear reactor core andconfigured to exchange a selected volume of the molten fuel salt with aselected volume of a feed material containing a mixture of a selectedfertile material and a carrier salt.

Another example molten salt reactor of any preceding reactor provides amolten fuel salt exchange system that includes a feed-fuel supply unitconfigured to transfer the feed material into the nuclear reactor core.

Another example molten salt reactor of any preceding reactor provides amolten fuel salt exchange system that a feed-fuel supply unit configuredto transfer a selected volume of the feed material into the nuclearreactor core.

Another example molten salt reactor of any preceding reactor provides amolten fuel salt exchange system that the molten fuel salt exchangesystem that includes a feed-fuel supply unit configured to transfer aselected composition of the feed material into the nuclear reactor core.

Another example molten salt reactor of any preceding reactor provides amolten fuel salt exchange system that includes a used-fuel transfer unitconfigured to transfer the selected volume of the molten fuel salt asused-fuel from the nuclear reactor core.

Another example molten salt reactor of any preceding reactor provides amolten fuel salt exchange system that is configured to transferconcurrently the selected volume of the molten fuel salt from thenuclear reactor core and the feed material into the nuclear reactorcore.

Another example molten salt reactor of any preceding reactor provides amolten fuel salt exchange system that controls reactivity of the nuclearfission reaction by exchanging the feed material with the selectedvolume of the molten fuel salt in the nuclear reactor core.

Another example molten salt reactor of any preceding reactor provides amolten fuel salt exchange system that controls composition of the moltenfuel salt in the nuclear fission reaction by exchanging the feedmaterial with the selected volume of the molten fuel salt in the nuclearreactor core.

Another example molten salt reactor of any preceding reactor provides afast spectrum fission reactor and the molten fuel salt includes achloride salt.

Another example molten salt reactor of any preceding reactor provides amolten fuel salt exchange system controls a composition ofUCl3-UCl4-NaCl in the spectrum fission reaction by exchanging the feedmaterial with the selected volume of the molten fuel salt in the nuclearreactor core.

Another example molten salt reactor of any preceding reactor provides amolten fuel salt exchange system is configured to exchange repeatedly aselected volume of the molten fuel salt with a selected volume of thefeed material to maintain the parameter indicative of reactivity of themolten salt reactor within a selected range of nominal reactivity overtime.

Another example molten salt reactor of any preceding reactor furtherincludes a reactivity parameter sensor positioned proximate the nuclearreactor core. The nuclear parameter sensor is configured to monitor oneor more parameters indicative of reactivity of the nuclear reactor core.A controller communicatively couples to the reactivity parameter sensorto receive the one or more parameters indicative of reactivity of thenuclear reactor core. The controller is configured to control exchangeof the selected volume of the molten fuel salt with the selected volumeof a feed material containing a mixture of a selected fertile materialand a carrier salt based on the one or more parameters.

Another example molten salt reactor of any preceding reactor providesthe molten fuel salt control system to further include a volumetricdisplacement control system having one or more volumetric displacementassemblies insertable into the nuclear reactor core. Each volumetricdisplacement assembly is configured to volumetrically displace aselected volume molten fuel salt from the nuclear reactor core wheninserted into the nuclear reactor core.

Another example molten salt reactor of any preceding reactor providesthe molten fuel salt control system to further include a volumetricdisplacement control system having one or more volumetric displacementbodies insertable into the nuclear reactor core, each volumetricdisplacement body being configured to volumetrically displace a selectedvolume of molten fuel salt from the nuclear reactor core when insertedinto the nuclear reactor core.

Another example molten salt reactor of any preceding reactor providesthe molten fuel salt control system to further include a volumetricdisplacement control system having one or more volumetric displacementbodies insertable into the nuclear reactor core, each volumetricdisplacement body being configured to volumetrically displace a selectedvolume of molten fuel salt from the nuclear reactor core when insertedinto the nuclear reactor core, the volumetric displacement controlsystem further having molten fuel salt spill-over system configured totransport molten fuel salt that is displaced by the volumetricdisplacement body above a tolerated fill level of the nuclear reactorcore.

Another example molten salt reactor of any preceding reactor providesthe molten fuel salt control system to further include a volumetricdisplacement control system having one or more volumetric displacementbodies insertable into the nuclear reactor core, each volumetricdisplacement body being configured to volumetrically displace a selectedvolume of molten fuel salt from the nuclear reactor core when insertedinto the nuclear reactor core, the volumetric displacement controlsystem being insertable at multiple insertion depths into the nuclearreactor core to maintain the parameter indicative of reactivity of themolten salt reactor within a selected range of nominal reactivity overtime.

Another molten salt nuclear reactor includes a nuclear reactor coreconfigured to sustain a nuclear fission reaction fueled by a molten fuelsalt and means for exchanging a selected volume of the molten fuel saltwith a selected volume of a feed material containing a mixture of aselected fertile material and a carrier salt.

Another molten salt nuclear reactor includes a nuclear reactor coreconfigured to sustain a nuclear fission reaction fueled by a molten fuelsalt and means for removing a selected volume of the molten fuel saltfrom the nuclear reactor core to maintain a parameter indicative ofreactivity of the molten salt reactor within a selected range of nominalreactivity.

An example method includes sustaining a nuclear fission reaction fueledby a molten fuel salt within a nuclear reactor core and removing aselected volume of the molten fuel salt from the nuclear reactor core tomaintain a parameter indicative of reactivity of the molten salt reactorwithin a selected range of nominal reactivity.

Another example method of any preceding method further includesreplacing the selected volume of the molten fuel salt with a selectedvolume of a feed material containing a mixture of a selected fertilematerial and a carrier salt.

Another example method of any preceding method wherein the replacingoperation includes transferring the feed material into the nuclearreactor core.

Another example method of any preceding method wherein the replacingoperation includes transferring a selected volume of the feed materialinto the nuclear reactor core.

Another example method of any preceding method wherein the replacingoperation includes transferring a selected composition of the feedmaterial into the nuclear reactor core.

Another example method of any preceding method wherein the replacingoperation includes controlling the reactivity of the nuclear reactorcore based on the selected volume of the feed material.

Another example method of any preceding method wherein the replacingoperation includes controlling the composition of the molten fuel saltfueling the nuclear fission reaction within the nuclear reactor corebased on the selected composition of the feed material.

Another example method of any preceding method wherein the replacingoperation includes controlling the composition of the UCl3-UCl4-NaClfueling the nuclear fission reaction within the nuclear reactor corebased on the selected composition of the feed material.

Another example method of any preceding method wherein the methodfurther includes monitoring satisfaction of an exchange condition by themolten fuel salt and controlling exchange of the selected volume of themolten fuel salt with the selected volume of a feed material containinga mixture of a selected fertile material and a carrier salt responsiveto satisfaction of the exchange condition.

Another example method of any preceding method wherein the methodfurther includes monitoring one or more reactivity parameters indicativeof reactivity of the nuclear reactor core and controlling exchange ofthe selected volume of the molten fuel salt with the selected volume ofa feed material containing a mixture of a selected fertile material anda carrier salt based on the one or more reactivity parameters.

Another example method of any preceding method wherein the methodfurther includes monitoring one or more composition parametersindicative of composition of the molten fuel salt of the nuclear reactorcore and controlling exchange of the selected volume of the molten fuelsalt with the selected volume of a feed material containing a mixture ofa selected fertile material and a carrier salt based on the one or morecomposition parameters.

Another example method of any preceding method wherein the removingoperation includes volumetrically displacing the selected volume moltenfuel salt from the nuclear reactor core by inserting one or morevolumetric displacement bodies into molten fuel salt within the nuclearreactor core.

Another example method of any preceding method wherein the removingoperation includes transporting the volumetrically displaced volume ofmolten fuel salt from the nuclear reactor core via a molten fuel saltspill-over system when the volumetrically displaced volume of moltenfuel salt is displaced by the volumetric displacement body above atolerated fill level of the nuclear reactor core.

Another example method of any preceding method provides a method whereineach volumetric displacement body is configured to volumetricallydisplace a selected volume of molten fuel salt from the nuclear reactorcore when inserted into the nuclear reactor core, the volumetricdisplacement control system being insertable at multiple insertiondepths into the nuclear reactor core to maintain the parameterindicative of reactivity of the molten salt reactor within a selectedrange of nominal reactivity over time.

An example fast spectrum molten salt nuclear reactor includes a reactorcore section including a fuel input and a fuel output, the fuel inputand the fuel output arranged to flow a molten chloride salt nuclear fuelthrough the reactor core section. The molten chloride salt nuclear fuelincluding a mixture of UCl₄ and at least one of an additional uraniumchloride salt or an additional metal chloride salt, the mixture of UCl₄and at least one additional metal chloride salt having a UCl₄ contentgreater than 5% by molar fraction.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the uranium concentration in the mixture ofUCl₄ and at least one additional metal chloride salt is greater than 61%by weight.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the additional uranium chloride saltincluding UCl₃.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the mixture of UCl₄ and at least one of anadditional uranium chloride salt or an additional metal chloride salthas a composition of 82UCl₄-18UCl₃.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the mixture of UCl₄ and at least one of anadditional uranium chloride salt or an additional metal chloride salthas a composition of 17UCl₃-71UCl₄-12NaCl.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the mixture of UCl₄ and at least one of anadditional uranium chloride salt or an additional metal chloride salthas a composition of 50 UCl₄-50NaCl.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the additional metal chloride including atleast one of NaCl, MgCl₂, CaCl₂, BaCl₂, KCl, SrCl₂, VCl₃, CrCl₃, TiCl₄,ZrCl₄, ThCl₄, AcCl₃, NpCl₄, PuCl₃, AmCl₃, LaCl₃, CeCl₃, PrCl₃ or NdCl₃.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the mixture of UCl₄ and at least one of anadditional uranium chloride salt or an additional metal chloride salthas an additional metal chloride salt concentration at or below theprecipitation concentration for the an additional metal chloride salt.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the mixture of UCl₄ and at least one of anadditional uranium chloride salt or an additional metal chloride salthaving a melting temperature below a temperature of ₈₀₀ degrees Celsius.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the mixture of UCl₄ and at least one of anadditional uranium chloride salt or an additional metal chloride salthaving the selected melting temperature above a temperature of 330degrees Celsius.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides breed-and-burn behavior established withinthe molten chloride salt nuclear fuel with a uranium-plutonium cycle.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the fuel input located on a first side of thereactor core section and the fuel output located on a second side of thereactor core section opposite to the fuel input.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides a protective layer disposed on at least onesurface facing the molten chloride salt nuclear fuel.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides that the at least one surface exposed to themolten chloride salt nuclear includes an internal surface of the reactorcore section.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the protective layer that is substantiallyresistant to at least one of corrosion or radiation.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the protective layer including at least oneof a refractory alloy, a nickel alloy, a refractory metal or siliconcarbide.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor includes a reflector assembly configured to reflect atleast a portion of neutrons emanating from the reactor core section backto the molten chloride salt nuclear fuel within the reactor coresection, the reflector assembly including a plurality of reflectormodules, at least some of the reflector modules containing a liquidreflector material.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides at least one of the reflector modules formedfrom at least one of a molybdenum alloy, a nickel alloy or a carbide.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the liquid reflector material including atleast one of liquid lead or liquid lead-bismuth.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor includes a displacement assembly operably coupled tothe reactor core section and configured to selectively displace a volumeof the molten salt nuclear fuel in order to control reactivity withinthe molten salt nuclear fuel.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the displacement assembly configured todisplace a volume of the molten salt nuclear fuel in order to reducereactivity within the molten salt nuclear fuel.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the displacement assembly that includes adisplacement element, an actuator operably coupled to the displacementelement, and a controller. The controller is configured to selectivelydirect the actuator to control a position of the displacement element inorder to control the reactivity within the molten salt nuclear fuelcontained within the reactor core section.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the displacement element that is formed froma substantially non-neutron-absorbing material.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor includes a molten salt transfer assembly.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the molten salt transfer assembly to includea molten salt transfer unit fluidically coupled to the reactor coresection and configured to transfer a selected portion of the moltenchloride salt fuel from a portion of the fast spectrum molten saltnuclear reactor to a reservoir. The molten salt transfer unit is furtherconfigured to transfer a feed material including at least some fertilematerial from a feed material supply to a portion of the fast spectrummolten salt nuclear reactor.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the at least some fertile material of thefeed material that includes at least one fertile fuel salt.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the at least one fertile fuel salt in includea salt containing at least one of depleted uranium, natural uranium orthorium.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the at least one fertile fuel salt to includea salt containing at least one metal from a used nuclear fuel.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor includes a fission product removal unit configured toremove at least one fission product from the molten chloride salt fuel.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor includes a primary coolant loop fluidically coupled tothe input of the nuclear core section and the output of the nuclear coresection.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor includes a primary heat exchanger and a secondarycoolant loop, the primary coolant loop and the secondary coolant loopthermally coupled via the primary heat exchanger.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor includes at least one pump disposed along the primarycoolant loop to circulate the molten chloride salt nuclear fuel throughthe primary coolant loop.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the at least pump that circulates the moltenchloride salt nuclear fuel through the primary coolant loop at or belowa selected flow velocity limit.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor includes a gas sparging unit configured to remove oneor more noble gases from the molten chloride salt nuclear fuel.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor includes a filter unit configured to remove at leastone of a noble metal or a semi-noble metal from the molten salt nuclearfuel.

A example method of fueling a fast spectrum molten salt nuclear reactorincludes providing a volume of UCl₄, providing a volume of at least oneof an additional uranium chloride salt or an additional metal chloridesalt, mixing the volume of UCl₄ with the volume of the at least one ofan additional uranium chloride salt or an additional metal chloride saltto form a molten chloride salt nuclear fuel having a UCl₄ contentgreater than 5% by molar fraction, and supplying the molten chloridesalt nuclear fuel having a UCl₄ content greater than 5% by molarfraction to at least a reactor core section of the fast spectrum moltensalt nuclear reactor.

Another example method of any preceding method includes providing avolume of at least one of an additional uranium chloride salt or anadditional metal chloride salt by providing a volume of UCl₃.

Another example method of any preceding method includes providing avolume of at least one of an additional uranium chloride salt or anadditional metal chloride salt by providing a volume of at least one ofNaCl, MgCl₂, CaCl₂, BaCl₂, KCl, SrCl₂, VCl₃, CrCl₃, TiCl₄, ZrCl₄, ThCl₄,AcCl₃, NpCl₄, PuCl₃, AmCl₃, LaCl₃, CeCl₃, PrCl₃ or NdC₁₃.

Another example method of any preceding method includes providing themixing the volume of UCl₄ with the volume of the at least one of anadditional uranium chloride salt or an additional metal chloride salt toform a molten chloride salt nuclear fuel having a UCl₄ content greaterthan 5% by molar fraction by mixing the volume of UCl₄ with the volumeof the at least one of an additional uranium chloride salt or anadditional metal chloride salt to form a molten chloride salt nuclearfuel having a UCl₄ content greater than 5% by molar fraction and amelting temperature between 330 and 800° C.

Another example method of any preceding method includes providing themixing the volume of UCl₄ with the volume of the at least one of anadditional uranium chloride salt or an additional metal chloride salt toform a molten chloride salt nuclear fuel having a UCl₄ content greaterthan 5% by molar fraction by mixing the volume of UCl₄ with the volumeof the at least one of an additional uranium chloride salt or anadditional metal chloride salt to form a molten chloride salt nuclearfuel having a composition of 82UCl₄-18UCl₃.

Another example method of any preceding method includes providing themixing the volume of UCl₄ with the volume of the at least one of anadditional uranium chloride salt or an additional metal chloride salt toform a molten chloride salt nuclear fuel having a UCl₄ content greaterthan 5% by molar fraction by mixing the volume of UCl₄ with the volumeof the at least one of an additional uranium chloride salt or anadditional metal chloride salt to form a molten chloride salt nuclearfuel having a composition of 17UCl₃-71UCl₄-12NaCl.

Another example method of any preceding method includes providing themixing the volume of UCl₄ with the volume of the at least one of anadditional uranium chloride salt or an additional metal chloride salt toform a molten chloride salt nuclear fuel having a UCl₄ content greaterthan 5% by molar fraction by mixing the volume of UCl₄ with the volumeof the at least one of an additional uranium chloride salt or anadditional metal chloride salt to form a molten chloride salt nuclearfuel having a composition of 50 UCl₄-50NaCl.

Another example method of any preceding method includes providing themixing the volume of UCl₄ with the volume of the at least one of anadditional uranium chloride salt or an additional metal chloride salt bymixing the volume of UCl₄ with the volume of the at least one of anadditional uranium chloride salt or an additional metal chloride saltinside of the fast spectrum molten salt nuclear reactor.

Another example method of any preceding method includes providing themixing the volume of UCl₄ with the volume of the at least one of anadditional uranium chloride salt or an additional metal chloride salt bymixing the volume of UCl₄ with the volume of the at least one of anadditional uranium chloride salt or an additional metal chloride saltoutside of the fast spectrum molten salt nuclear reactor.

An example molten chloride salt fuel for use in a fast spectrum moltensalt nuclear reactor prepared by a process including providing a volumeof UCl₄, providing a volume of at least one of an additional uraniumchloride salt or an additional metal chloride salt, and mixing thevolume of UCl₄ with the volume of the at least one of an additionaluranium chloride salt or an additional metal chloride salt to form amolten chloride salt nuclear fuel having a UCl₄ content greater than 5%by molar fraction.

An example fast spectrum molten salt nuclear reactor includes a reactorcore section including a fuel input and a fuel output. The fuel inputand the fuel output are arranged to flow a mixture of molten saltnuclear fuel and at least one lanthanide through the reactor coresection at start-up of the fast spectrum molten salt nuclear reactor.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the at least one lanthanide that includes atleast one of La, Ce, Pr or Nd.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the mixture of molten salt nuclear fuel andat least one lanthanide that includes a mixture of molten salt nuclearfuel and at least one lanthanide formed by mixing the molten saltnuclear fuel with at least one lanthanide chloride.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the at least one lanthanide chloride thatincludes at least one of LaCl₃, CeCl₃, PrCl₃ or NdCl₃.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the mixture of molten salt nuclear fuel andat least one lanthanide that includes a mixture of molten salt nuclearfuel and at least one lanthanide having a lanthanide concentrationbetween 0.1 and 10% by weight.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the mixture of molten salt nuclear fuel andat least one lanthanide having a lanthanide concentration between 0.1and 10% by weight that includes a mixture of molten salt nuclear fueland at least one lanthanide having a lanthanide concentration between 4and 8% by weight.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the mixture of molten salt nuclear fuel andthe at least one lanthanide that is formed outside of the fast spectrummolten salt nuclear reactor.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the mixture of molten salt nuclear fuel andthe at least one lanthanide that is formed inside of the fast spectrummolten salt nuclear reactor.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the fuel input and the fuel output that arearranged to flow a mixture of molten salt nuclear fuel and at least onelanthanide through the reactor core section prior to achieving aselected reactivity threshold in the fast spectrum molten salt nuclearreactor.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the fuel input and the fuel output that arearranged to flow a mixture of molten salt nuclear fuel and at least onelanthanide through the reactor core section prior to achievingcriticality in the fast spectrum molten salt nuclear reactor.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the fuel input and the fuel output that arearranged to flow a mixture of molten salt nuclear fuel and at least onelanthanide through the reactor core section prior to generation of aselected amount of plutonium in the fast spectrum molten salt nuclearreactor.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the molten salt nuclear fuel that includes amixture of at least two of a first uranium chloride, a second uraniumchloride or an additional metal chloride.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the additional metal chloride that includesat least one of NaCl, MgCl₂, CaCl₂, BaCl₂, KCl, SrCl₂, VCl₃, CrCl₃,TiCl₄, ZrCl₄, ThCl₄, AcCl₃, NpCl₄, PuCl₃ or AmCl₃.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides at least one of the first uranium chloride orthe second uranium chloride that includes at least one of UCl₄ or UCl₃.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the molten salt nuclear fuel that has acomposition of 82UCl₄-18UCl₃.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the molten salt nuclear fuel that has acomposition of 17UCl₃-71UCl₄-12NaCl.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the molten salt nuclear fuel that has acomposition of 50 UCl₄-50NaCl.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the molten salt nuclear fuel that has acomposition of 34 UCl₃-66NaCl.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the mixture of at least a first uraniumchloride, a second uranium chloride and an additional metal chloridethat includes at least 5% by molar fraction UCl₄.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the mixture of at least a first uraniumchloride, a second uranium chloride and an additional metal chloridethat has a uranium concentration of greater than 61% by weight.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the mixture of at least a first uraniumchloride, a second uranium chloride and an additional metal chloridethat has a melting point between 330 and 800 degrees Celsius.

An example method of fueling a fast spectrum molten salt nuclear reactorincludes providing a molten salt nuclear fuel and providing at least onelanthanide. Prior to start-up of the fast spectrum molten salt nuclearreactor, the molten salt nuclear fuel is mixed with the at least onelanthanide to form a lanthanide-loaded molten salt nuclear fuel. Thelanthanide-loaded molten salt nuclear fuel is supplied to at least areactor core section of the fast spectrum molten salt nuclear reactor.

Another example method of any preceding method provides a molten saltnuclear fuel by providing a mixture of at least two of a first uraniumchloride, an additional uranium chloride and an additional metalchloride.

Another example method of any preceding method provides a molten saltnuclear fuel by providing a mixture of at least two of UCl₄, UCl₃ and anadditional metal chloride.

Another example method of any preceding method provides the additionalmetal chloride to include at least one of NaCl, MgCl₂, CaCl₂, BaCl₂,KCl, SrCl₂, VCl₃, CrCl₃, TiCl₄, ZrCl₄, ThCl₄, AcCl₃, NpCl₄, PuCl₃ orAmCl₃.

Another example method of any preceding method provides a molten saltnuclear fuel by providing a molten salt nuclear fuel having at least 5%by molar fraction UCl₄.

Another example method of any preceding method provides a molten saltnuclear fuel by providing a molten salt nuclear fuel having a uraniumconcentration of greater than 61% by weight.

Another example method of any preceding method provides a molten saltnuclear fuel by providing a molten salt nuclear fuel having a meltingpoint between 330 and 800 degrees Celsius.

Another example method of any preceding method provides at least onelanthanide by providing at least one of La, Ce, Pr or Nd.

Another example method of any preceding method provides at least onelanthanide by providing at least one lanthanide in the form of alanthanide chloride.

Another example method of any preceding method provides at least onelanthanide in the form of a lanthanide chloride by providing at leastone of LaCl₃, CeCl₃, PrCl₃ or NdCl₃.

Another example method of any preceding method provides mixing of themolten salt nuclear fuel with the at least one lanthanide to form alanthanide-loaded molten salt nuclear fuel by mixing the molten saltnuclear fuel with the at least one lanthanide to form alanthanide-loaded molten salt nuclear fuel having a lanthanideconcentration between 0.1 and 10% by weight.

Another example method of any preceding method provides mixing of themolten salt nuclear fuel with the at least one lanthanide to form alanthanide-loaded molten salt nuclear fuel having a lanthanideconcentration between 0.1 and 10% by weight by mixing the molten saltnuclear fuel with the at least one lanthanide to form alanthanide-loaded molten salt nuclear fuel having a lanthanideconcentration between 4 and 8% by weight.

Another example method of any preceding method provides mixing of themolten salt nuclear fuel with the at least one lanthanide to form alanthanide-loaded molten salt nuclear fuel by mixing the molten saltnuclear fuel with the at least one lanthanide outside of the fastspectrum molten salt nuclear reactor.

Another example method of any preceding method provides mixing of themolten salt nuclear fuel with the at least one lanthanide to form alanthanide-loaded molten salt nuclear fuel by mixing the molten saltnuclear fuel with the at least one lanthanide inside of the fastspectrum molten salt nuclear reactor.

Another example method of any preceding method provides, prior tostart-up of the fast spectrum molten salt nuclear reactor, the mixing ofthe molten salt nuclear fuel with the at least one lanthanide to form alanthanide-loaded molten salt nuclear fuel by, prior to achieving aselected reactivity threshold in the fast spectrum molten salt nuclearreactor, mixing the molten salt nuclear fuel with the at least onelanthanide to form a lanthanide-loaded molten salt nuclear fuel.

Another example method of any preceding method provides, prior tostart-up of the fast spectrum molten salt nuclear reactor, mixing of themolten salt nuclear fuel with the at least one lanthanide to form alanthanide-loaded molten salt nuclear fuel by, prior to achievingcriticality in the fast spectrum molten salt nuclear reactor, mixing themolten salt nuclear fuel with the at least one lanthanide to form alanthanide-loaded molten salt nuclear fuel.

Another example method of any preceding method provides, prior tostart-up of the fast spectrum molten salt nuclear reactor, mixing of themolten salt nuclear fuel with the at least one lanthanide to form alanthanide-loaded molten salt nuclear fuel by, prior to generation of aselected amount of plutonium in the fast spectrum molten salt nuclearreactor, mixing the molten salt nuclear fuel with the at least onelanthanide to form a lanthanide-loaded molten salt nuclear fuel.

An example molten salt fuel for use in a fast spectrum molten saltnuclear reactor prepared by a processing that includes providing amolten salt nuclear fuel, providing at least one lanthanide, and priorto start-up of the fast spectrum molten salt nuclear reactor, mixing themolten salt nuclear fuel with the at least one lanthanide to form alanthanide-loaded molten salt nuclear fuel.

An example fast spectrum molten salt nuclear reactor includes a reactorcore section including a fuel input and a fuel output. The fuel inputand the fuel output are arranged to flow a molten salt nuclear fuelthrough the reactor core section. A displacement assembly is operablycoupled to the reactor core section and configured to selectivelydisplace a volume of the molten salt nuclear fuel in order to controlreactivity within the molten salt nuclear fuel.

Another example fast spectrum molten salt nuclear reactor of anypreceding claim provides the displacement assembly as configured toselectively displace a volume of the molten salt nuclear fuel at acentral region of the reactor core section.

Another example fast spectrum molten salt nuclear reactor of anypreceding claim provides the displacement assembly as configured todisplace a volume of the molten salt nuclear fuel in order to reducereactivity within the molten salt nuclear fuel.

Another example fast spectrum molten salt nuclear reactor of anypreceding claim provides the displacement assembly to include adisplacement element, an actuator operably coupled to the displacementelement, and a controller. The controller is configured to selectivelydirect the actuator to control a position of the displacement element inorder to control the reactivity within the molten salt nuclear fuelcontained within the reactor core section.

Another example fast spectrum molten salt nuclear reactor of anypreceding claim provides the displacement element and the reactorsection to be centered along a common axis.

Another example fast spectrum molten salt nuclear reactor of anypreceding claim provides the actuator as configured to drive thedisplacement assembly into the reactor core section in order to reducethe reactivity within the molten salt nuclear fuel.

Another example fast spectrum molten salt nuclear reactor of anypreceding claim provides the actuator as configured to withdraw thedisplacement assembly from the reactor core section in order to increasethe reactivity within the molten salt nuclear fuel.

Another example fast spectrum molten salt nuclear reactor of anypreceding claim includes a reactivity parameter sensor configured tosense at least one reactivity parameter of the molten chloride saltnuclear fuel, wherein the reactivity parameter sensor is communicativelycoupled to the controller.

Another example fast spectrum molten salt nuclear reactor of anypreceding claim provides the reactivity parameter sensor that includesat least one of a fission detector, a neutron flux monitor, a neutronfluence sensor, a fission product sensor, a temperature sensor, apressure sensor or a power sensor.

Another example fast spectrum molten salt nuclear reactor of anypreceding claim provides the controller as configured to selectivelydirect the actuator to control the position of the displacement elementwithin the reactor core section in response to at least one sensedreactivity parameter of the molten chloride salt nuclear fuel from thereactivity parameter sensor.

Another example fast spectrum molten salt nuclear reactor of anypreceding claim provides the displacement element that includes adisplacement rod.

Another example fast spectrum molten salt nuclear reactor of anypreceding claim provides the displacement element that includes aplurality of displacement rods.

Another example fast spectrum molten salt nuclear reactor of anypreceding claim provides the displacement element as formed from asubstantially non-neutron-absorbing material.

Another example fast spectrum molten salt nuclear reactor of anypreceding claim provides the displacement element as formed from atleast one of a substantially neutron-transparent material or asubstantially neutron-reflective material.

Another example fast spectrum molten salt nuclear reactor of anypreceding claim includes a spill-over system configured to transportexcess molten salt nuclear fuel out of the reactor core section.

Another example fast spectrum molten salt nuclear reactor of anypreceding claim provides the spill-over system that includes a fuel saltuptake. The fuel salt uptake is positioned above a selected maximummolten salt nuclear fuel fill level of the reactor core section andconfigured to transport excess molten salt nuclear fuel out of thereactor core section. At least one fluid transport element and aspill-over reservoir are also included. The at least one fluid transportelement fluidically couples the fuel salt uptake and the spill-overreservoir. The spill-over reservoir is configured to store excess moltensalt nuclear fuel received from the at least one fluid transportelement.

Another example fast spectrum molten salt nuclear reactor of anypreceding claim provides the molten salt nuclear fuel that includes amixture of at least two of a first uranium chloride, a second uraniumchloride or an additional metal chloride.

Another example fast spectrum molten salt nuclear reactor of anypreceding claim provides the additional metal chloride that includes atleast one of NaCl, MgCl₂, CaCl₂, BaCl₂, KCl, SrCl₂, VCl₃, CrCl₃, TiCl₄,ZrCl₄, ThCl₄, AcCl₃, NpCl₄, PuCl₃, AmCl₃, LaCl₃, CeCl₃, PrCl₃ or NdCl₃.

Another example fast spectrum molten salt nuclear reactor of anypreceding claim provides at least one of the first uranium chloride orthe second uranium chloride that includes at least one of UCl₄ or UCl₃.

Another example fast spectrum molten salt nuclear reactor of anypreceding claim provides the molten salt nuclear fuel that has acomposition of 82UCl₄-18UCl₃.

Another example fast spectrum molten salt nuclear reactor of anypreceding claim provides the molten salt nuclear fuel that has acomposition of 17UCl₃-71UCl₄-12NaCl.

Another example fast spectrum molten salt nuclear reactor of anypreceding claim provides the molten salt nuclear fuel that has acomposition of 50 UCl₄-50NaCl.

Another example fast spectrum molten salt nuclear reactor of anypreceding claim provides the molten salt nuclear fuel that has acomposition of 34 UCl₃-66NaCl.

Another example fast spectrum molten salt nuclear reactor of anypreceding claim provides the mixture of at least a first uraniumchloride, a second uranium chloride and an additional metal chloridethat includes at least 5% by molar fraction UCl₄.

Another example fast spectrum molten salt nuclear reactor of anypreceding claim provides the mixture of at least a first uraniumchloride, a second uranium chloride and an additional metal chloridethat has a uranium concentration of greater than 61% by weight.

Another example fast spectrum molten salt nuclear reactor of anypreceding claim provides the mixture of at least a first uraniumchloride, a second uranium chloride and an additional metal chloridethat has a melting point between 330 and 800 degrees Celsius.

Another example fast spectrum molten salt nuclear reactor of anypreceding claim provides the molten salt nuclear fuel that includes amixture of at least one uranium fluoride and an additional metalfluoride.

An example method includes determining a reactivity parameter in amolten salt nuclear fuel of a molten salt nuclear reactor and,responsive to the reactivity parameter in the molten salt nuclear fuel,displacing a selected volume of the molten salt nuclear fuel with atleast one displacement element to control the reactivity of the moltensalt nuclear fuel.

Another example method of any preceding method provides the determininga reactivity parameter in a molten salt nuclear fuel of a molten saltnuclear reactor by acquiring at least one of a neutron production rate,a neutron absorption rate, a neutron flux, a neutron fluence, atemperature, a pressure, a power or a fission product production rate ofthe molten salt nuclear fuel, and determining a reactivity parameter inthe molten salt nuclear fuel of a molten salt nuclear reactor based onthe at least one of a neutron production rate, a neutron absorptionrate, a neutron flux, a neutron fluence, a temperature, a pressure, apower or a fission product production rate.

Another example method of any preceding method provides, responsive to areactivity parameter in the molten salt nuclear fuel, displacing aselected volume of the molten salt nuclear fuel with at least onedisplacement element to adjust the reactivity of the molten salt nuclearfuel by responsive to a reactivity parameter indicative of excessreactivity in the molten salt nuclear reactor, displacing a selectedvolume of the molten salt nuclear fuel with at least one displacementelement to reduce the reactivity of the molten salt nuclear reactor.

Another example method of any preceding method provides displacing aselected volume of the molten salt nuclear fuel with at least onedisplacement element by displacing a selected volume of the molten saltnuclear fuel by driving at least a portion of at least one displacementelement into the molten salt nuclear fuel to reduce the reactivity ofthe molten salt nuclear reactor.

Another example method of any preceding method provides displacing aselected volume of the molten salt nuclear fuel with at least onedisplacement element by displacing a selected volume of the molten saltnuclear fuel by withdrawing at least a portion of at least onedisplacement element from the molten salt nuclear fuel to increase thereactivity of the molten salt nuclear reactor.

Another example method of any preceding method provides displacing aselected volume of the molten salt nuclear fuel by driving at least aportion of at least one displacement element into the molten saltnuclear fuel by displacing a selected volume of the molten salt nuclearfuel by driving a selected amount of at least one displacement elementinto the molten salt nuclear fuel, wherein the selected amount is basedon the determined reactivity parameter.

Another example method of any preceding method provides displacing aselected volume of the molten salt nuclear fuel by driving at least aportion of at least one displacement element into the molten saltnuclear fuel by displacing a selected volume of the molten salt nuclearfuel by driving at least a portion of at least one displacement elementinto a volume of the molten salt nuclear fuel within a reactor coresection of the molten salt nuclear reactor.

Another example method of any preceding method provides displacing aselected volume of the molten salt nuclear fuel by driving at least aportion of at least one displacement element into a volume of the moltensalt nuclear fuel within a reactor core section of the molten saltnuclear reactor by displacing a selected volume of the molten saltnuclear fuel by driving at least a portion of at least one displacementelement into a volume of the molten salt nuclear fuel at a centralregion of the reactor core section of the molten salt nuclear reactor.

Another example method of any preceding method provides displacing aselected volume of the molten salt nuclear fuel with at least onedisplacement element by displacing a selected volume of the molten saltnuclear fuel with at least one displacement rod.

Another example method of any preceding method provides displacing aselected volume of the molten salt nuclear fuel with at least onedisplacement rod by displacing a selected volume of the molten saltnuclear fuel with at least one hollow displacement rod.

Another example method of any preceding method provides displacing aselected volume of the molten salt nuclear fuel with at least onedisplacement rod by displacing a selected volume of the molten saltnuclear fuel with at least one solid displacement rod.

Another example method of any preceding method provides displacing aselected volume of the molten salt nuclear fuel with at least onedisplacement rod by displacing a selected volume of the molten saltnuclear fuel with a plurality of displacement rods.

Another example method of any preceding method provides the at least onedisplacement rod that is formed from at least one of lead or tungsten.

Another example method of any preceding method provides the displacing aselected volume of the molten salt nuclear fuel with at least onedisplacement element by displacing a selected volume of the molten saltnuclear fuel with at least one displacement rod formed from asubstantially non-neutron-absorbing material.

Another example method of any preceding method provides the displacing aselected volume of the molten salt nuclear fuel with at least onedisplacement element by displacing between 0.1 and 10 cubic meters ofthe molten salt nuclear fuel with at least one displacement element.

Another example method of any preceding method provides determining areactivity parameter in a molten salt nuclear fuel of a molten saltnuclear reactor by determining a reactivity parameter in a molten saltnuclear fuel including a mixture of at least two of a first uraniumchloride, an additional uranium chloride or an additional metalchloride.

Another example method of any preceding method provides determining areactivity parameter in a molten salt nuclear fuel including a mixtureof at least two of a first uranium chloride, an additional uraniumchloride or an additional metal chloride by determining a reactivityparameter in a molten salt nuclear fuel including a mixture of at leasttwo of a first uranium chloride, an additional uranium chloride or anadditional metal chloride a mixture of at least two of UCl₄, UCl₃ and anadditional metal chloride.

Another example method of any preceding method provides the additionalmetal chloride that includes at least one of NaCl, MgCl₂, CaCl₂, BaCl₂,KCl, SrCl₂, VCl₃, CrCl₃, TiCl₄, ZrCl₄, ThCl₄, AcCl₃, NpCl₄, PuCl₃,AmCl₃, LaCl₃, CeCl₃, PrCl₃ or NdCl₃.

Another example method of any preceding method provides determining areactivity parameter in a molten salt nuclear fuel by determining areactivity parameter in a molten salt nuclear fuel having at least 5% bymolar fraction UCl₄.

Another example method of any preceding method provides the determininga reactivity parameter in a molten salt nuclear fuel by determining areactivity parameter in a molten salt nuclear fuel having a uraniumconcentration of greater than 61% by weight.

Another example method of any preceding method provides determining areactivity parameter in a molten salt nuclear fuel by determining areactivity parameter in a molten salt nuclear fuel having a meltingpoint between 330 and 800 degrees Celsius.

An example fast spectrum molten salt nuclear reactor includes a reactorcore section including a fuel input and a fuel output, the fuel inputand the fuel output arranged to flow a molten salt nuclear fuel throughthe reactor core section and a molten fuel salt exchange assemblyoperably coupled to the reaction core section and configured to replacea selected volume of the molten salt nuclear fuel with a selected volumeof feed material to control the reactivity of the molten salt nuclearreactor. The molten salt nuclear fuel includes at least some fissilematerial. The feed material includes at least some fertile material.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the selected volume of feed material that issubstantially equal in volume to the selected volume of the molten saltnuclear fuel.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the replaced selected volume of the moltensalt nuclear fuel that includes at least some fission products.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the at least some fission products thatincludes one or more lanthanides.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the replaced selected volume of the moltensalt nuclear fuel that includes a carrier salt.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the molten fuel salt exchange assembly thatincludes a used-fuel transfer unit fluidically coupled to the reactorcore section and configured to transfer a selected volume of the moltensalt fuel from the reactor core section to a reservoir and a feed-fuelsupply unit fluidically coupled to the reactor core section andconfigured to transfer a selected volume of feed material including atleast some fertile material from a feed material source to the reactorcore section.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor that includes a controller is configured toselectively direct the used-fuel unit to transfer a selected volume ofthe molten salt fuel from the reactor core section to a reservoir and toselectively direct the feed-fuel supply unit to transfer a feed materialincluding at least some fertile material from a feed material source toa portion of the reactor core section.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor that includes a reactivity parameter sensor configuredto sense at least one reactivity parameter of the molten salt nuclearfuel, wherein the reactivity parameter sensor is communicatively coupledto the controller.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the controller as configured to selectivelydirect the used-fuel transfer unit to transfer a selected volume of themolten salt fuel from the reactor core section to a reservoir and thecontroller is further configured to selectively direct the feed-fuelsupply unit to transfer a feed material including at least some fertilematerial from a feed material source to a portion of the reactor coresection in response to at least one sensed reactivity parameter of themolten salt nuclear fuel from the reactivity parameter sensor.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the reactivity parameter sensor that includesat least one of a fission detector, a neutron flux monitor, a neutronfluence sensor, a fission product sensor, a temperature sensor, apressure sensor or a power sensor.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the reservoir that includes at least one of astorage reservoir.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the reservoir that includes at least onesecond generation molten salt reactor.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the at least some fertile material of thefeed material that includes at least one fertile fuel salt.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the at least one fertile fuel salt thatincludes a salt containing at least one of depleted uranium, naturaluranium or thorium.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the at least one fertile fuel salt thatincludes a salt containing at least one metal from a used nuclear fuel.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the molten salt nuclear fuel that includes amixture of at least a first uranium chloride, a second uranium chlorideand an additional metal chloride.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the additional metal chloride that includesat least one of NaCl, MgCl₂, CaCl₂, BaCl₂, KCl, SrCl₂, VCl₃, CrCl₃,TiCl₄, ZrCl₄, ThCl₄, AcCl₃, NpCl₄, PuCl₃, AmCl₃, LaCl₃, CeCl₃, PrCl₃ orNdCl₃.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides at least one of the first uranium chloride orthe second uranium chloride that includes at least one of UCl₄ or UCl₃.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the molten salt nuclear fuel that has acomposition of 82UCl₄-18UCl₃.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the molten salt nuclear fuel that has acomposition of 17UCl₃-71UCl₄-12NaCl.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the molten salt nuclear fuel that has acomposition of 50 UCl₄-50NaCl.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the molten salt nuclear fuel that has acomposition of 34 UCl₃-66NaCl.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the mixture of at least a first uraniumchloride, a second uranium chloride and an additional metal chloridethat includes at least 5% by molar fraction UCl₄.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the mixture of at least a first uraniumchloride, a second uranium chloride and an additional metal chloridethat has a uranium concentration of greater than 61% by weight.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the mixture of at least a first uraniumchloride, a second uranium chloride and an additional metal chloridethat has a melting point between 330 and 800 degrees Celsius.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the molten salt nuclear fuel that includes amixture of at least one uranium fluoride and an additional metalfluoride.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor includes a gas sparging unit configured to remove anoble gas from the molten salt nuclear fuel.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor includes a filter unit configured to remove at leastone of a noble metal or a semi-noble metal from the molten salt nuclearfuel.

An example method includes operating a molten salt fast spectrum nuclearreactor including a molten salt nuclear fuel and replacing a selectedvolume of the molten salt nuclear fuel with a selected volume of feedmaterial to control the reactivity of the molten salt nuclear reactor.The molten salt nuclear fuel includes at least some fissile material.The feed material includes at least some fertile material.

Another example method of any preceding method provides replacing aselected volume of the molten salt nuclear fuel with a selected volumeof feed material by replacing a selected volume of the molten saltnuclear fuel with a selected volume of feed material equal in volume tothe selected volume of the molten salt nuclear reactor.

Another example method of any preceding method provides replacing aselected volume of the molten salt nuclear fuel with a selected volumeof feed material by replacing a selected volume of the molten saltnuclear fuel including at least some fission products with a selectedvolume of feed material.

Another example method of any preceding method provides replacing aselected volume of the molten salt nuclear fuel including at least somefission products with a selected volume of feed material by replacing aselected volume of the molten salt nuclear fuel including one or morelanthanides with a selected volume of feed material.

Another example method of any preceding method provides replacing aselected volume of the molten salt nuclear fuel with a selected volumeof feed material by replacing a selected volume of the molten saltnuclear fuel including a carrier salt with a selected volume of feedmaterial.

Another example method of any preceding method provides replacing aselected volume of the molten salt nuclear fuel with a selected volumeof feed material to control the reactivity of the molten salt nuclearreactor by replacing a selected volume of the molten salt nuclear fuelwith a selected volume of feed material to maintain the reactivity ofthe molten salt nuclear fuel of molten salt nuclear reactor.

Another example method of any preceding method includes measuring areactivity parameter of the molten salt nuclear fuel of the molten saltfast spectrum nuclear reactor.

Another example method of any preceding method provides replacing aselected volume of the molten salt nuclear fuel with a selected volumeof feed material to control the reactivity of the molten salt nuclearreactor by, responsive to the measured reactivity parameter of themolten salt nuclear fuel, replacing a selected volume of the molten saltnuclear fuel with a selected volume of feed material to control thereactivity of the molten salt nuclear reactor.

Another example method of any preceding method provides measuring areactivity parameter of the molten salt nuclear fuel of the molten saltfast spectrum nuclear reactor by measuring at least one of a neutronproduction rate, a neutron absorption rate, a neutron flux, a neutronfluence, a temperature, a pressure, a power or a fission productproduction rate of the molten salt nuclear fuel of the molten salt fastspectrum nuclear reactor.

Another example method of any preceding method provides replacing aselected volume of the molten salt nuclear fuel with a selected volumeof feed material to control the reactivity of the molten salt nuclearreactor by continuously replacing a selected volume of the molten saltnuclear fuel with a selected volume of feed material to control thereactivity of the molten salt nuclear reactor.

Another example method of any preceding method provides replacing aselected volume of the molten salt nuclear fuel with a selected volumeof feed material to control the reactivity of the molten salt nuclearreactor by repeatedly replacing a selected batch volume of the moltenchloride salt nuclear fuel with a selected volume of feed material tocontrol the reactivity of the molten salt nuclear reactor.

Another example method of any preceding method provides replacing aselected volume of the molten salt nuclear fuel with a selected volumeof feed material to control the reactivity of the molten salt nuclearreactor, the molten salt nuclear fuel including at least some fissilematerial, the feed material including at least some fertile material byremoving a selected volume of the molten salt nuclear fuel from the fastspectrum molten salt nuclear reactor, the removed selected volume ofmolten salt nuclear fuel including at least some fissile material, andsupplying a selected volume of feed material to the fast spectrum moltensalt nuclear reactor, the supplied selected volume of feed materialincluding at least some fertile material.

Another example method of any preceding method provides a rate of supplyof the selected volume of feed material that is selected to match a rateof addition of fertile material into the molten salt nuclear reactor toa rate of burning of fissile material within the molten salt nuclearreactor.

Another example method of any preceding method provides the removedselected volume of the molten salt nuclear fuel that further includes atleast one of a fission product, a fertile material or a carrier salt.

Another example method of any preceding method provides the at leastsome fertile material of the feed material that includes at least onefertile fuel salt.

Another example method of any preceding method provides the at least onefertile fuel salt that includes a salt containing at least one ofdepleted uranium, natural uranium or thorium.

Another example method of any preceding method provides the at least onefertile fuel salt that includes a salt containing at least one metalfrom a used nuclear fuel.

Another example method of any preceding method provides the at least onefertile fuel salt that maintains a chemical composition of the moltensalt reactor fuel.

Another example method of any preceding method includes removing a noblegas from the molten salt nuclear fuel via a gas sparging process.

Another example method of any preceding method includes removing atleast one of a noble metal or a semi-noble metal from the molten saltnuclear fuel via a plating process.

An example system includes at least one first generation molten saltnuclear reactor including a molten salt nuclear fuel, at least onesecond generation molten salt nuclear reactor, and a molten salttransfer unit configured to transfer a volume of molten salt nuclearfuel from the at least one first generation molten salt nuclear reactorto at least one second generation molten salt nuclear reactor. Thevolume of the molten salt nuclear fuel includes at least some fissilematerial enriched in the at least one first generation molten saltnuclear reactor.

Another example system of any preceding system provides the volume ofthe molten salt nuclear fuel including at least some fissile materialthat is enriched in the at least one first generation molten saltnuclear reactor to so as to achieve criticality in the at least onesecond generation molten nuclear reactor.

Another example system of any preceding system provides the volume ofthe molten salt nuclear fuel including at least some fissile materialthat is enriched in the at least one first generation molten saltnuclear reactor to so as to achieve criticality in the at least onesecond generation molten nuclear reactor without enrichment of thevolume of the molten salt nuclear fuel in the at least one secondgeneration molten nuclear reactor.

Another example system of any preceding system provides operation of theat least one first generation molten salt nuclear reactor to enrich atleast some uranium to generate Pu-239 within the at least one firstgeneration molten salt nuclear reactor.

Another example system of any preceding system provides the volume ofmolten salt nuclear fuel transferred from the at least one firstgeneration molten salt nuclear reactor to the at least one secondgeneration molten salt nuclear reactor that includes Pu-239 generatedwithin the at least one first generation molten salt nuclear reactor.

Another example system of any preceding system provides the molten salttransfer unit that includes a fission product removal system configuredto remove one or more fission products from the volume of molten saltnuclear fuel from the at least one first generation molten salt nuclearreactor.

Another example system of any preceding system provides the at least onefirst generation molten salt nuclear reactor that includes: a pluralityof first generation molten salt nuclear reactors.

Another example system of any preceding system provides the at least onesecond generation molten salt nuclear reactor that includes a pluralityof second generation molten salt nuclear reactors.

Another example system of any preceding system provides the molten saltnuclear fuel of the at least one first generation molten salt nuclearreactor that includes a mixture of at least two of a first uraniumchloride, a second uranium chloride or an additional metal chloride.

Another example system of any preceding system provides the additionalmetal chloride that includes at least one of NaCl, MgCl₂, CaCl₂, BaCl₂,KCl, SrCl₂, VCl₃, CrCl₃, TiCl₄, ZrCl₄, ThCl₄, AcCl₃, NpCl₄, PuCl₃,AmCl₃, LaCl₃, CeCl₃, PrCl₃ or NdCl₃.

Another example system of any preceding system provides at least one ofthe first uranium chloride or the second uranium chloride that includesat least one of UCl₄ or UCl₃.

Another example system of any preceding system provides the molten saltnuclear fuel that has a composition of 82UCl₄-18UCl₃.

Another example system of any preceding system provides the molten saltnuclear fuel that has a composition of 17UCl₃-71UCl₄-12NaCl.

Another example system of any preceding system provides the molten saltnuclear fuel that has a composition of 50 UCl₄-50NaCl.

Another example system of any preceding system provides the molten saltnuclear fuel that has a composition of 34 UCl₃-66NaCl.

Another example system of any preceding system provides the mixture ofat least two of a first uranium chloride, a second uranium chloride oran additional metal chloride that includes at least 5% by molar fractionUCl₄.

Another example system of any preceding system provides the mixture ofat least two of a first uranium chloride, a second uranium chloride oran additional metal chloride that has a uranium concentration of greaterthan 61% by weight.

Another example system of any preceding system provides the mixture ofat least two of a first uranium chloride, a second uranium chloride oran additional metal chloride that has a melting point between 330 and800 degrees Celsius.

Another example system of any preceding system provides the molten saltnuclear fuel of the at least one first generation molten salt nuclearreactor that includes a mixture of at least one uranium fluoride and anadditional metal fluoride.

An example method includes enriching at least a portion of a molten saltnuclear fuel in at least one first generation molten salt nuclearreactor, removing a volume of the enriched molten salt nuclear fuel fromthe at least one first generation molten salt nuclear reactor, andsupplying at least a portion of the removed volume of molten saltnuclear fuel from the at least one first generation molten salt nuclearreactor to at least one second generation molten salt nuclear reactor.

Another example method of any preceding method provides enriching atleast a portion of a molten salt nuclear fuel in at least one firstgeneration molten salt nuclear reactor by enriching at least a portionof a molten salt nuclear fuel in at least one first generation moltensalt nuclear reactor so as to achieve criticality in the at least onesecond generation molten nuclear reactor.

Another example method of any preceding method provides enriching atleast a portion of a molten salt nuclear fuel in at least one firstgeneration molten salt nuclear reactor so as to achieve criticality inthe at least one second generation molten nuclear reactor by enrichingat least a portion of a molten salt nuclear fuel in at least one firstgeneration molten salt nuclear reactor so as to achieve criticality inthe at least one second generation molten nuclear reactor withoutenrichment of the volume of the molten salt nuclear fuel in the at leastone second generation molten nuclear reactor.

Another example method of any preceding method provides enriching atleast a portion of a molten salt nuclear fuel in at least one firstgeneration molten salt nuclear reactor by enriching at least someuranium within a volume of the molten salt nuclear fuel of the at leastone first generation molten salt nuclear reactor to generate Pu-239.

Another example method of any preceding method incudes removing one ormore fission products from the at least a portion of the volume ofmolten salt nuclear fuel removed from the at least one first generationmolten salt nuclear reactor.

Another example method of any preceding method provides supplying atleast a portion of the removed volume of molten salt nuclear fuel fromthe at least one first generation molten salt nuclear reactor to atleast one second generation molten salt nuclear reactor by supplying aportion of the removed volume of molten salt nuclear fuel from the atleast one first generation molten fast spectrum salt nuclear reactor toa first second generation molten salt nuclear reactor and supplying atleast one additional portion of the removed volume of molten saltnuclear fuel from the at least one first generation fast spectrum moltensalt nuclear reactor to at least one additional second generation moltensalt nuclear reactor.

Another example method of any preceding method provides removing avolume of the enriched molten salt nuclear fuel from the at least onefirst generation molten salt nuclear reactor by removing a volume ofmolten salt nuclear fuel from at least one first generation molten saltnuclear reactor to control reactivity of the at least one firstgeneration molten salt nuclear reactor.

Another example method of any preceding method provides removing avolume of the enriched molten salt nuclear fuel from the at least onefirst generation molten salt nuclear reactor by continuously removing avolume of the enriched molten salt nuclear fuel from the at least onefirst generation molten salt nuclear reactor.

Another example method of any preceding method provides removing avolume of the enriched molten salt nuclear fuel from the at least onefirst generation molten salt nuclear reactor by repeatedly removing aselected batch of a volume of the enriched molten salt nuclear fuel fromthe at least one first generation molten salt nuclear reactor.

Another example method of any preceding method that includes supplying aselected volume of feed material to the at least one first generationmolten salt nuclear reactor, the feed material including at least somefertile material.

Another example method of any preceding method provides the at leastsome fertile material of the feed material that includes at least onefertile fuel salt.

Another example method of any preceding method provides the at least onefertile fuel salt that includes a salt containing at least one ofdepleted uranium, natural uranium or thorium.

Another example method of any preceding method provides the at least onefertile fuel salt that includes a salt containing at least one metalfrom a used nuclear fuel.

Another example method of any preceding method provides the at least onefertile fuel salt that maintains a chemical composition of the moltensalt reactor fuel. Another example method of any preceding methodincludes supplying a selected volume of feed material to the at leastone second generation molten salt nuclear reactor, the feed materialincluding at least some fertile material.

An example fast spectrum molten salt nuclear reactor includes a reactorcore section including a fuel input and a fuel output. The fuel inputand the fuel output are arranged to flow a molten chloride salt nuclearfuel through the reactor core section. The molten chloride salt nuclearfuel includes a mixture of UCl₄ and at least one of an additionaluranium chloride salt or an additional metal chloride salt, the mixtureof UCl₄ and at least one additional metal chloride salt having a UCl₄content greater than 5% by molar fraction.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the uranium concentration in the mixture ofUCl₄ and at least one additional metal chloride salt that is greaterthan 61% by weight.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the additional uranium chloride salt thatincludes UCl₃.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the mixture of UCl₄ and at least one of anadditional uranium chloride salt or an additional metal chloride salthas a composition of 82UCl₄-18UCl₃.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the mixture of UCl₄ and at least one of anadditional uranium chloride salt or an additional metal chloride saltthat has a composition of 17UCl₃-71UCl₄-12NaCl.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the mixture of UCl₄ and at least one of anadditional uranium chloride salt or an additional metal chloride saltthat has a composition of 50 UCl₄-50NaCl.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the mixture of UCl₄ and at least one of anadditional uranium chloride salt or an additional metal chloride saltthat has an additional metal chloride salt concentration at or below theprecipitation concentration for the additional metal chloride salt.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the mixture of UCl₄ and at least one of anadditional uranium chloride salt or an additional metal chloride saltthat has a melting temperature below a temperature of 800 degreesCelsius.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides the selected melting temperature that isabove a temperature of 330 degrees Celsius.

Another example fast spectrum molten salt nuclear reactor of anypreceding reactor provides breed-and-burn behavior that is establishedwithin the molten chloride salt nuclear fuel with a uranium-plutoniumcycle.

An example method of fueling a fast spectrum molten salt nuclear reactorincludes providing a volume of UCl₄, providing a volume of at least oneof an additional uranium chloride salt or an additional metal chloridesalt, mixing the volume of UCl₄ with the volume of the at least one ofan additional uranium chloride salt or an additional metal chloride saltto form a molten chloride salt nuclear fuel having a UCl₄ contentgreater than 5% by molar fraction, and supplying the molten chloridesalt nuclear fuel having a UCl₄ content greater than 5% by molarfraction to at least a reactor core section of the fast spectrum moltensalt nuclear reactor.

Another example method of any preceding method provides a volume of atleast one of an additional uranium chloride salt or an additional metalchloride salt by providing a volume of UCl₃.

Another example method of any preceding method provides the chlorine inthe UCl₄ that is enriched with 37Cl.

Another example method of any preceding method provides the chlorine inthe salt that is enriched to at least 75% 37Cl.

The above specification, examples, and data provide a completedescription of the structure and use of exemplary implementations of theinvention. Since many implementations of the invention can be madewithout departing from the spirit and scope of the invention, theinvention resides in the claims hereinafter appended. Furthermore,structural features of the different implementations may be combined inyet another implementation without departing from the recited claims.

1-34. (canceled)
 35. A method of controlling reactivity of a nuclearfission reaction in a molten salt reactor having a nuclear reactor corecomprising: sustaining a nuclear fission reaction fueled by a moltenfuel salt within the nuclear reactor core; monitoring one or morereactivity parameters indicative of reactivity of the molten fuel saltwithin the nuclear reactor core, the one or more reactivity parametersincluding a first parameter; and maintaining the first parameterindicative of reactivity of the molten fuel salt within the nuclearreactor core within a selected range of nominal reactivity by replacinga first volume of the molten fuel salt with a second volume of a feedmaterial that does not contain any fissile material.
 36. The method ofclaim 35 wherein the first volume and the second volume are the same.37. The method of claim 35 wherein the feed material consists of amixture of a selected fertile material and salt.
 38. The method of claim35 wherein replacing comprises: removing the first volume of molten fuelsalt from the molten salt reactor; and transferring the second volume ofthe feed material into the molten salt reactor.
 39. The method of claim38 wherein removing comprises: volumetrically displacing the firstvolume of molten fuel salt from by inserting one or more volumetricdisplacement bodies into molten fuel salt within the molten saltreactor.
 40. The method of claim 39 wherein removing comprises:transporting the first volume of molten fuel salt via a molten fuel saltspill-over system when molten fuel salt is displaced by the one or morevolumetric displacement bodies above a fill level of the molten saltreactor.
 41. The method of claim 39 wherein the one or more volumetricdisplacement bodies are configured to volumetrically displace a selectedvolume of molten fuel salt from the nuclear reactor core when insertedinto the nuclear reactor core.
 42. The method of claim 35 furthercomprising: determining the second volume of the feed material to beadded to the nuclear reactor core necessary to bring the first parameterwithin the selected range.
 43. The method of claim 35 furthercomprising: determining a composition of the feed material to be addedto the nuclear reactor core necessary to bring the first parameterwithin the selected range.
 44. The method of claim 35 furthercomprising: controlling a composition of the molten fuel salt fuelingthe nuclear fission reaction within the nuclear reactor core byreplacing the first volume of the molten fuel salt with the secondvolume of a feed material that does not contain any fissile material.45. The method of claim 44 wherein controlling comprises: selecting atarget fuel salt composition for the molten fuel salt in the nuclearreactor core, the target fuel salt composition different from a currentmolten fuel salt composition; determining the first volume of currentmolten fuel salt composition to remove from the molten fuel salt, thesecond volume of the feed material to be added to the nuclear fuel salt,and the composition of feed material necessary to change the currentmolten fuel salt composition to the target fuel salt composition. 46.The method of claim 44 further comprising: monitoring the composition ofthe molten fuel salt.
 47. The method of claim 44 wherein the target fuelsalt composition is a salt containing UCl₃, UCl₄, NaCl and some amountof fission products and the feed material is a salt consisting of one ormore of UCl₃, UCl₄, and NaCl.
 48. The method of claim 35 wherein thefirst parameter indicative of reactivity of the molten fuel salt withinthe nuclear reactor core is k_(eff) and the selected range of nominalreactivity is from 1.0 to 1.035.
 49. The method of claim 35 wherein thefirst parameter indicative of reactivity of the molten fuel salt withinthe nuclear reactor core is k_(eff) and the selected range of nominalreactivity is from 1.001 to 1.005.
 50. The method of claim 35 whereinthe first parameter indicative of reactivity of the molten fuel saltwithin the nuclear reactor core is k_(eff) and the selected range ofnominal reactivity is from 1.0 to 1.01.
 51. The method of claim 35further comprising: monitoring one or more of neutron fluence, neutronflux, neutron fissions, fission products, radioactive decay events,temperature, pressure, power, isotropic concentration, burn-up andneutron spectrum.
 52. The method of claim 35 further comprising:monitoring the one or more reactivity parameters indicative ofreactivity of the nuclear reactor core; and controlling exchange of thefirst volume of the molten fuel salt with the second volume of a feedmaterial, wherein the feed material consists of a mixture of a selectedfertile material and salt based on the one or more reactivityparameters.
 53. The method of claim 35 further comprising: monitoringone or more composition parameters indicative of composition of themolten fuel salt of the nuclear reactor core; and controlling exchangeof the first volume of the molten fuel salt with the second volume of afeed material containing a mixture of a selected fertile material andsalt based on the one or more composition parameters.
 54. The method ofclaim 35 wherein the feed material consists of UCl₃ and one or more ofUCl₄, NaCl, MgCl₂, CaCl₂, BaCl₂, KCl, SrCl₂, VCl₃, CrCl₃, TiCl₄, ZrCl₄,ThCl₄, AcCl₃, NpCl₄, PuCl₃, AmCl₃, LaCl₃, CeCl₃, PrCl₃, and/or NdCl₃.